Method for transmitting and receiving downlink signals between terminal and base station in wireless communication system supporting unlicensed band, and device supporting same

ABSTRACT

Disclosed are a method for transmitting and receiving downlink signals between a terminal and a base station in a wireless communication system supporting an unlicensed band, and a device supporting same. More specifically, as one applicable embodiment in the present disclosure, the terminal can control/change a monitoring period of a physical downlink control channel on the basis of whether a downlink signal transmission burst is transmitted from a base station, and in response thereto, the base station sets a transmission period of the physical downlink control channel in the downlink signal transmission burst so as to transmit the same to the terminal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/877,725, filed on May 19, 2020, which is a continuation ofInternational Application No. PCT/KR2019/000751, filed on Jan. 18, 2019,which claims the benefit of Korean Application No. 10-2018-0092781,filed on Aug. 9, 2018, and U.S. Provisional Application No. 62/619,044,filed on Jan. 18, 2018. The disclosures of the prior applications areincorporated by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to a wireless communication system, andmore particularly, to a method of transmitting and receiving a downlinksignal between a terminal and a base station in a wireless communicationsystem supporting an unlicensed band and devices for supporting thesame.

BACKGROUND ART

Wireless access systems have been widely deployed to provide varioustypes of communication services such as voice or data. In general, awireless access system is a multiple access system that supportscommunication of multiple users by sharing available system resources (abandwidth, transmission power, etc.) among them. For example, multipleaccess systems include a code division multiple access (CDMA) system, afrequency division multiple access (FDMA) system, a time divisionmultiple access (TDMA) system, an orthogonal frequency division multipleaccess (OFDMA) system, and a single carrier frequency division multipleaccess (SC-FDMA) system.

As a number of communication devices have required higher communicationcapacity, the necessity of the mobile broadband communication muchimproved than the existing radio access technology (RAT) has increased.In addition, massive machine type communications (MTC) capable ofproviding various services at anytime and anywhere by connecting anumber of devices or things to each other has been considered in thenext generation communication system. Moreover, a communication systemdesign capable of supporting services/UEs sensitive to reliability andlatency has been discussed.

As described above, the introduction of the next generation RATconsidering the enhanced mobile broadband communication, massive MTC,ultra-reliable and low latency communication (URLLC), and the like hasbeen discussed.

SUMMARY

An aspect of the present disclosure devised to solve the conventionalproblem is to provide a method and apparatus for transmitting andreceiving a downlink signal between a terminal and a base station (BS)in a wireless communication system supporting an unlicensed band.

It will be appreciated by persons skilled in the art that the objectsthat could be achieved with the present disclosure are not limited towhat has been particularly described hereinabove and the above and otherobjects that the present disclosure could achieve will be more clearlyunderstood from the following detailed description.

The present disclosure provides a method of transmitting and receiving adownlink signal between a user equipment and a base station in awireless communication system supporting an unlicensed band and devicesfor supporting the same.

In an aspect of the present disclosure, provided is a method ofreceiving a downlink signal by a user equipment (UE) from a base station(BS) in a wireless communication system supporting an unlicensed band.The method may include: receiving the downlink signal by performingfirst physical downlink control channel (PDCCH) monitoring at a firstperiodicity in the unlicensed band; receiving an initial signalindicating the presence of a downlink transmission burst from the BS inthe unlicensed band; and receiving the downlink signal by performingsecond PDCCH monitoring at a second periodicity different from the firstperiodicity in the unlicensed band, wherein the second PDCCH monitoringmay be performed from a slot after N slots with respect to a slot inwhich the initial signal is received during transmission of the downlinktransmission burst,

The second periodicity may correspond to one slot duration.

The second PDCCH monitoring based on the second periodicity may includemonitoring a PDCCH at the second periodicity at a slot boundary at whicheach slot starts.

The first periodicity may be shorter than the second periodicity.

The first periodicity may be indicated or configured by physical layersignaling or higher layer signaling.

First PDCCH candidates for the first PDCCH monitoring based on the firstperiodicity at the slot boundary at which each slot starts may have arelationship of inclusion with second PDCCH candidates for the secondPDCCH monitoring based on the second periodicity.

In the present disclosure, the initial signal may be one of thefollowing:

-   -   a synchronization signal modified for extension in the frequency        domain;    -   a demodulation reference signal (DM-RS) for a physical broadcast        channel (PBCH) modified for the extension in the frequency        domain;    -   a DM-RS for the PDCCH;    -   a group common PDCCH;    -   a cell-specific channel state information reference signal        (CSI-RS); and    -   a cyclic prefix (CP) for some symbols of the downlink        transmission burst or a part of the CP.

The group common PDCCH may include slot format indicator (SFI)information.

In this case, receiving, by the UE, the group common PDCCH as theinitial signal may include: detecting a DM-RS for the group commonPDCCH; decoding the group common PDCCH based on the DM-RS; and obtainingthe presence of the downlink transmission burst from the BS by checkingwhether a cyclic redundancy check (CRC) result for the group commonPDCCH is successful.

In another aspect of the present disclosure, provided is a method oftransmitting a downlink signal by a base station (BS) to a userequipment (UE) in a wireless communication system supporting anunlicensed band. The method may include: performing a channel accessprocedure (CAP) for transmitting the downlink signal in the unlicensedband; and transmitting an initial signal and a downlink transmissionburst including a physical downlink control channel (PDCCH) in theunlicensed band based on the CAP. The PDCCH included in the downlinktransmission burst may be transmitted to the UE at a predeterminedperiodicity during the transmission of the downlink transmission burst.

The predetermine periodicity may correspond to one slot duration.

In the present disclosure, the initial signal may be one of thefollowing:

-   -   a synchronization signal modified for extension in a frequency        domain;    -   a demodulation reference signal (DM-RS) for a physical broadcast        channel (PBCH) modified for the extension in the frequency        domain;    -   a DM-RS for the PDCCH;    -   a group common PDCCH;    -   a cell-specific channel state information reference signal        (CSI-RS); and    -   a cyclic prefix (CP) for some symbols of the downlink        transmission burst or a part of the CP.

The group common PDCCH may include slot format indicator (SFI)information.

In still another aspect of the present disclosure, provided is acommunication device for receiving a downlink signal from a base station(BS) in a wireless communication system supporting an unlicensed band.The communication device may include a memory and a processor connectedto the memory. The processor may be configured to: receive the downlinksignal by performing first physical downlink control channel (PDCCH)monitoring at a first periodicity in the unlicensed band; receive aninitial signal informing the presence of a downlink transmission burstfrom the BS in the unlicensed band; and receive the downlink signal byperforming second PDCCH monitoring at a second periodicity differentfrom the first periodicity in the unlicensed band, wherein the secondPDCCH monitoring may be performed from a slot after N slots with respectto a slot in which the initial signal is received during transmission ofthe downlink transmission burst.

Additionally or alternatively, the communication device is a part of anautonomous driving device that communicates with at least one of anetwork or another autonomous driving vehicle.

In a further aspect of the present disclosure, provided is acommunication device for transmitting a downlink signal to a userequipment (UE) in a wireless communication system supporting anunlicensed band. The communication device may include a memory and aprocessor connected to the memory. The processor may be configured to:perform a channel access procedure (CAP) for transmitting the downlinksignal in the unlicensed band; and transmit an initial signal and adownlink transmission burst including a physical downlink controlchannel (PDCCH) in the unlicensed band based on the CAP. The PDCCHincluded in the downlink transmission burst may be transmitted to the UEat a predetermined periodicity during the transmission of the downlinktransmission burst.

It is to be understood that both the foregoing general description andthe following detailed description of the present disclosure areexemplary and explanatory and are intended to provide furtherexplanation of the disclosure as claimed.

As is apparent from the above description, the embodiments of thepresent disclosure have the following effects.

According to the present disclosure, a UE may recognize/obtain based onan initial signal transmitted from a BS whether there is a downlinktransmission burst to be transmitted from the BS in an unlicensed bandand adaptively adjust the periodicity of PDCCH monitoring based on suchrecognition, thereby improving the power saving spectral efficiency ofthe UE.

It will be appreciated by persons skilled in the art that the effectsthat could be achieved with the present disclosure are not limited towhat has been particularly described hereinabove and other advantages ofthe present disclosure will be more clearly understood from thefollowing detailed description. That is, effects which are not intendedby the present disclosure may be derived by those skilled in the artfrom the embodiments of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the disclosure, provide embodiments of the presentdisclosure together with detail explanation. Yet, a technicalcharacteristic of the present disclosure is not limited to a specificdrawing. Characteristics disclosed in each of the drawings are combinedwith each other to configure a new embodiment. Reference numerals ineach drawing correspond to structural elements.

FIG. 1 is a diagram illustrating physical channels and a signaltransmission method using the physical channels.

FIGS. 2A and 2B are diagrams illustrating radio frame structures.

FIG. 3 is a diagram illustrating frame structure type 3.

FIG. 4 is a diagram illustrating a resource grid for a downlink slot.

FIG. 5 is a diagram illustrating an uplink subframe structure.

FIG. 6 is a diagram illustrating a downlink subframe structure.

FIG. 7 is a diagram for explaining the concept of dual connectivityapplicable to the present disclosure.

FIG. 8 is a diagram illustrating a self-contained slot structureapplicable to the present disclosure.

FIGS. 9 and 10 are diagrams illustrating representative methods ofconnecting transceiver units (TXRUs) to antenna elements.

FIG. 11 is a schematic diagram illustrating a hybrid beamformingstructure from the perspective of TXRUs and physical antennas accordingto an example of the present disclosure.

FIG. 12 is a schematic diagram illustrating a beam sweeping operationfor a synchronization signal and system information in a downlinktransmission procedure according to an example of the presentdisclosure.

FIG. 13 is a schematic diagram illustrating a synchronizationsignal/physical broadcast channel (SS/PBCH) block applicable to thepresent disclosure.

FIG. 14 is a schematic diagram illustrating an SS/PBCH blocktransmission configuration applicable to the present disclosure.

FIGS. 15A and 15B illustrate an exemplary wireless communication systemsupporting an unlicensed band, which is applicable to the presentdisclosure.

FIG. 16 is a diagram illustrating a channel access procedure (CAP) fortransmission in an unlicensed band, which is applicable to the presentdisclosure.

FIG. 17 is a diagram illustrating a partial TTI or a partial subframeapplicable to the present disclosure.

FIG. 18 is a diagram schematically illustrating a PDCCH monitoringoperation for a UE applicable to the present disclosure.

FIG. 19 is a diagram illustrating a signal transmission and receptionmethod for a UE and a BS in a unlicensed band applicable to the presentdisclosure, FIG. 20 is a flowchart illustrating a method for the UE toreceive a downlink signal in the unlicensed band applicable to thepresent disclosure, and FIG. 21 is a flowchart illustrating a method forthe BS to transmit the downlink signal in the unlicensed band applicableto the present disclosure.

FIG. 22 is a block diagram illustrating the configurations of a UE and aBS for implementing the proposed embodiments.

DETAILED DESCRIPTION

The embodiments of the present disclosure described below arecombinations of elements and features of the present disclosure inspecific forms. The elements or features may be considered selectiveunless otherwise mentioned. Each element or feature may be practicedwithout being combined with other elements or features. Further, anembodiment of the present disclosure may be constructed by combiningparts of the elements and/or features. Operation orders described inembodiments of the present disclosure may be rearranged. Someconstructions or elements of any one embodiment may be included inanother embodiment and may be replaced with corresponding constructionsor features of another embodiment.

In the description of the attached drawings, a detailed description ofknown procedures or steps of the present disclosure will be avoided lestit should obscure the subject matter of the present disclosure. Inaddition, procedures or steps that could be understood to those skilledin the art will not be described either.

Throughout the specification, when a certain portion “includes” or“comprises” a certain component, this indicates that other componentsare not excluded and may be further included unless otherwise noted. Theterms “unit”, “-or/er” and “module” described in the specificationindicate a unit for processing at least one function or operation, whichmay be implemented by hardware, software or a combination thereof. Inaddition, the terms “a or an”, “one”, “the” etc. may include a singularrepresentation and a plural representation in the context of the presentdisclosure (more particularly, in the context of the following claims)unless indicated otherwise in the specification or unless contextclearly indicates otherwise.

In the embodiments of the present disclosure, a description is mainlymade of a data transmission and reception relationship between a basestation (BS) and a user equipment (UE). A BS refers to a terminal nodeof a network, which directly communicates with a UE. A specificoperation described as being performed by the BS may be performed by anupper node of the BS.

Namely, it is apparent that, in a network comprised of a plurality ofnetwork nodes including a BS, various operations performed forcommunication with a UE may be performed by the BS, or network nodesother than the BS. The term ‘BS’ may be replaced with a fixed station, aNode B, an evolved Node B (eNode B or eNB), gNode B (gNB), an advancedbase station (ABS), an access point, etc.

In the embodiments of the present disclosure, the term terminal may bereplaced with a UE, a mobile station (MS), a subscriber station (SS), amobile subscriber station (MSS), a mobile terminal, an advanced mobilestation (AMS), etc.

A transmission end is a fixed and/or mobile node that provides a dataservice or a voice service and a reception end is a fixed and/or mobilenode that receives a data service or a voice service. Therefore, a UEmay serve as a transmission end and a BS may serve as a reception end,on an uplink (UL). Likewise, the UE may serve as a reception end and theBS may serve as a transmission end, on a downlink (DL).

The embodiments of the present disclosure may be supported by standardspecifications disclosed for at least one of wireless access systemsincluding an Institute of Electrical and Electronics Engineers (IEEE)802.xx system, a 3rd Generation Partnership Project (3GPP) system, a3GPP Long Term Evolution (LTE) system, 3GPP 5G NR system and a 3GPP2system. In particular, the embodiments of the present disclosure may besupported by the standard specifications, 3GPP TS 36.211, 3GPP TS36.212, 3GPP TS 36.213, 3GPP TS 36.321, 3GPP TS 36.331, 3GPP TS 37.213,3GPP TS 38.211, 3GPP TS 38.212, 3GPP TS 38.213, 3GPP TS 38.321 and 3GPPTS 38.331. That is, the steps or parts, which are not described toclearly reveal the technical idea of the present disclosure, in theembodiments of the present disclosure may be explained by the abovestandard specifications. All terms used in the embodiments of thepresent disclosure may be explained by the standard specifications.

Reference will now be made in detail to the embodiments of the presentdisclosure with reference to the accompanying drawings. The detaileddescription, which will be given below with reference to theaccompanying drawings, is intended to explain exemplary embodiments ofthe present disclosure, rather than to show the only embodiments thatcan be implemented according to the disclosure.

The following detailed description includes specific terms in order toprovide a thorough understanding of the present disclosure. However, itwill be apparent to those skilled in the art that the specific terms maybe replaced with other terms without departing the technical spirit andscope of the present disclosure.

Hereinafter, 3GPP LTE/LTE-A systems and 3GPP NR system are explained,which are examples of wireless access systems.

The embodiments of the present disclosure can be applied to variouswireless access systems such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), etc.

CDMA may be implemented as a radio technology such as UniversalTerrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implemented asa radio technology such as Global System for Mobile communications(GSM)/General packet Radio Service (GPRS)/Enhanced Data Rates for GSMEvolution (EDGE). OFDMA may be implemented as a radio technology such asIEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Evolved UTRA(E-UTRA), etc.

UTRA is a part of Universal Mobile Telecommunications System (UMTS).3GPP LTE is a part of Evolved UMTS (E-UMTS) using E-UTRA, adopting OFDMAfor DL and SC-FDMA for UL. LTE-Advanced (LTE-A) is an evolution of 3GPPLTE.

While the embodiments of the present disclosure are described in thecontext of 3GPP LTE/LTE-A systems and 3GPP NR system in order to clarifythe technical features of the present disclosure, the present disclosureis also applicable to an IEEE 802.16e/m system, etc.

1. 3GPP LTE/LTE-A SYSTEM

1.1. Physical Channels and Transmitting/Receiving Signal

In a wireless access system, a UE receives information from a basestation on a DL and transmits information to the base station on a UL.The information transmitted and received between the UE and the basestation includes general data information and various types of controlinformation. There are many physical channels according to thetypes/usages of information transmitted and received between the basestation and the UE.

FIG. 1 illustrates physical channels and a general signal transmissionmethod using the physical channels, which may be used in embodiments ofthe present disclosure.

When a UE is powered on or enters a new cell, the UE performs initialcell search (S11). The initial cell search involves acquisition ofsynchronization to a BS. Specifically, the UE synchronizes its timing tothe base station and acquires information such as a cell identifier (ID)by receiving a primary synchronization channel (P-SCH) and a secondarysynchronization channel (S-SCH) from the BS.

Then the UE may acquire information broadcast in the cell by receiving aphysical broadcast channel (PBCH) from the base station.

During the initial cell search, the UE may monitor a DL channel state byreceiving a Downlink Reference Signal (DL RS).

After the initial cell search, the UE may acquire more detailed systeminformation by receiving a physical downlink control channel (PDCCH) andreceiving on a physical downlink shared channel (PDSCH) based oninformation of the PDCCH (S12).

Subsequently, to complete connection to the eNB, the UE may perform arandom access procedure with the eNB (S13 to S16). In the random accessprocedure, the UE may transmit a preamble on a physical random accesschannel (PRACH) (S13) and may receive a PDCCH and a random accessresponse (RAR) for the preamble on a PDSCH associated with the PDCCH(S14). The UE may transmit a PUSCH by using scheduling information inthe RAR (S15), and perform a contention resolution procedure includingreception of a PDCCH signal and a PDSCH signal corresponding to thePDCCH signal (S16).

After the above procedure, the UE may receive a PDCCH and/or a PDSCHfrom the BS (S17) and transmit a physical uplink shared channel (PUSCH)and/or a physical uplink control channel (PUCCH) to the BS (S18), in ageneral UL/DL signal transmission procedure.

Control information that the UE transmits to the BS is genericallycalled uplink control information (UCI). The UCI includes a hybridautomatic repeat and request acknowledgement/negative acknowledgement(HARQ-ACK/NACK), a scheduling request (SR), a channel quality indicator(CQI), a precoding matrix index (PMI), a rank indicator (RI), etc.

In general, UCI is transmitted periodically on a PUCCH. However, ifcontrol information and traffic data should be transmittedsimultaneously, the control information and traffic data may betransmitted on a PUSCH. In addition, the UCI may be transmittedaperiodically on the PUSCH, upon receipt of a request/command from anetwork.

1.2. Radio Frame Structures

FIGS. 2A and 2B are diagrams illustrating radio frame structuresapplicable to the embodiments of the present disclosure.

FIG. 2A illustrates frame structure type 1. Frame type 1 is applicableto both a full frequency division duplex (FDD) system and a half FDDsystem.

One radio frame has a duration of T_(f)=307200*T_(s)=10 ms and includes20 slots, which are indexed from 0 to 19. Each of the slots has aduration of T_(slot)=15360*T_(s)=0.5 ms. One subframe is defined as twoconsecutive slots, and more specifically, subframe #i is defined as slot#2i and slot #2i+1. That is, a radio frame includes 10 subframes. Thetime required for transmitting one subframe is defined as a transmissiontime interval (TTI). T_(s) denotes a sampling time and is given asT_(s)=1/(15 kHz×2048)=3.2552×10⁻⁸ (about 33 ns). A slot includes aplurality of orthogonal frequency division multiplexing (OFDM) symbolsor single carrier orthogonal frequency division multiplexing (SC-FDMA)symbols in the time domain and a plurality of resource blocks (RBs) inthe frequency domain.

One slot includes a plurality of OFDM symbols in the time domain. SinceOFDMA is adopted for DL in the 3GPP LTE system, one OFDM symbolrepresents one symbol duration. An OFDM symbol may be replaced with anSC-FDMA symbol. An RB is a resource allocation unit including aplurality of consecutive subcarriers in one slot.

In the full FDD system, 10 subframes may be used for DL and ULtransmission at the same time for a duration of 10 ms. In this case, theDL and UL transmission may be separated in the frequency domain.However, in the half FDD system, a UE may not perform transmission andreception simultaneously.

The above-described radio frame structure is merely exemplary. Thus, thenumber of subframes in a radio frame, the number of slots in a subframe,or the number of OFDM symbols in a slot may be changed in variousmanners.

FIG. 2B illustrates frame structure type 2. Frame structure type 2 isapplied to a time division duplex (TDD) system. One radio frame has aduration of T_(f)=307200*T_(s)=10 ms and includes two half-frames, eachof which has a duration of 153600*T_(s)=5 ms. Each half-frame includes 5subframes each having a duration of 30720*T_(s)=1 ms. Subframe #iincludes two slots: slot #i and slot #2i+1, each having a duration ofT_(slot)=15360*T_(s)=0.5 ms, where Ts denotes a sampling time and isgiven as T_(s)=1/(15 kHz×2048)=3.2552×10⁻⁸ (about 33 ns).

A Type 2 frame includes a special subframe including three fields: adownlink pilot time slot (DwPTS), a guard period (GP), and an uplinkpilot time slot (UpPTS). The DwPTS is used for initial cell search,synchronization, or channel estimation at a UE, and the UpPTS is usedfor channel estimation at an eNB and acquisition of UL transmissionsynchronization at a UE. The GP is a period for cancelling ULinterference caused by DL signal multipath delay between DL and UL.

Table 1 below shows special subframe configurations (DwPTS/GP/UpPTSlengths).

TABLE 1 Normal cyclic prefix in downlink Extended cyclic prefix indownlink UpPTS UpPTS Special Normal Extended Normal Extended subframecyclic prefix cyclic prefix cyclic prefix cyclic prefix configurationDwPTS in uplink in uplink DwPTS in uplink in uplink 0  6592 · T_(s) 2192· T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 1 19760 ·T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 · T_(s) 25600· T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120 · T_(s) 5  6592· T_(s) 4384 · T_(s) 5120 · T_(s) 20480 · T_(s) 6 19760 · T_(s) 23040 ·T_(s) 7 21952 · T_(s) 12800 · T_(s) 8 24144 · T_(s) — — — 9 13168 ·T_(s) — — —

In the LTE Rel-13 system, it has been allowed to change the specialframe configurations (e.g., DwPTS/GP/UpPTS lengths) by considering thenumber of additional SC-FDMA symbols X (which is provided by the higherlayer parameter named srs-UpPtsAdd) (if this parameter is notconfigured, X is set to 0). In the LTE Rel-14 system, specific subframeconfiguration #10 has been newly added. A UE may expect not to beconfigured with two additional UpPTS SC-FDMA symbols for specialsubframe configurations {3, 4, 7, 8} with a normal cyclic prefix in DLfor special subframe configurations {3, 4, 7, 8} for a normal cyclicprefix (CP) in DL and special subframe configurations {2, 3, 5, 6} foran extended CP in DL. In addition, the UE may expect not to beconfigured with four additional UpPTS SC-FDMA symbols for specialsubframe configurations {1, 2, 3, 4, 6, 7, 8} for the normal CP in DLand special subframe configurations {1, 2, 3, 5, 6} for the extended CPin DL.

TABLE 2 Normal cyclic prefix in downlink Extended cyclic prefix indownlink UpPTS UpPTS Special Normal cyclic Extended cyclic NormalExtended subframe prefix prefix cyclic prefix cyclic prefixconfiguration DwPTS In uplink In uplink DwPTS in uplink in uplink 0 6592 · T_(s) (1 + X) · (1 + X) ·  7680 · T_(s) (1 + X) · (1 + X) · 119760 · T_(s)  2192 · T_(s)  2560 · T_(s) 20480 · T_(s) 2192 · T_(s)2560 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 · T_(s) 25600 · T_(s)4 26336 · T_(s)  7680 · T_(s) (2 + X) · (2 + X) · 5  6592 · T_(s) (2 +X) · (2 + X) · 20480 · T_(s) 2192 · T_(s) 2560 · T_(s) 6 19760 · T_(s) 2192 · T_(s)  2560 · T_(s) 23040 · T_(s) 7 21952 · T_(s) 12800 · T_(s)8 24144 · T_(s) — — — 9 13168 · T_(s) — — — 10 13168 · T_(s) 13152 ·T_(s) 12800 · T_(s) — — —

FIG. 3 is a diagram illustrating frame structure type 3.

Frame structure type 3 may be applied to UCell operation. Frame type 3may be applied to licensed assisted access (LAA) SCell operation with anormal CP, but it is not limited thereto. A frame has a duration of 10ms, and thus it is defined as 10 1-ms subframes. Subframe #i is definedas two consecutive slots: slot #2i and slot #2i+1. Each subframe may beused for DL or UL transmission or left empty. A DL burst occupies one ormore consecutive subframes, starting at any point in a subframe andending at the boundary thereof or in the DwPTS of Table 3. A UL burstalso occupies one or more consecutive subframes.

FIG. 4 illustrates a resource grid of a DL slot applicable to theembodiments of the present disclosure.

Referring to FIG. 4 , a DL slot includes a plurality of OFDM symbols inthe time domain. Although FIG. 4 illustrates that one DL slot includes 7OFDM symbols and one RB includes 12 subcarriers in the frequency domain,the present disclosure is not limited thereto.

Each element on the resource grid is referred to as a resource element(RE). One RB includes 12×7 REs. The number of RBs included in a DL slot,N^(DL) depends on a DL transmission bandwidth.

FIG. 5 illustrates a UL subframe structure applicable to the embodimentsof the present disclosure.

Referring to FIG. 5 , a UL subframe may be divided into a control regionand a data region in the frequency domain. A PUCCH carrying UCI isallocated to the control region, and a PUSCH carrying user data isallocated to the data region. A UE does not transmit the PUCCH and thePUSCH at the same time to maintain a single carrier property. For oneUE, the PUCCH is allocated to a pair of RBs in a subframe. The RBsbelonging to the RB pair occupy different subcarriers in two slots.Thus, it is said that the RB pair allocated as the PUCCH isfrequency-hopped in a slot boundary.

FIG. 6 illustrates a DL subframe structure applicable to the embodimentsof the present disclosure.

Referring to FIG. 6 , up to three OFDM symbols from OFDM symbol index 0of the first slot in a subframe may correspond to a control region inwhich control channels are allocated, and the remaining OFDM symbols maycorrespond to a data region in which a PDSCH is allocated. In the 3GPPLTE system, the following downlink control channels are used: a physicalcontrol format indicator channel (PCFICH), a PDCCH, a physicalhybrid-ARQ indicator channel (PHICH), etc.

The PCFICH is transmitted in the first OFDM symbol of a subframe,conveying information about the number of OFDM symbols (i.e., the sizeof a control region) used for transmission of control channels in thesubframe. The PHICH is a response channel for a UL transmission,conveying a hybrid automatic repeat request (HARD) acknowledgement(ACK)/negative acknowledgement (NACK) signal. Control informationdelivered on the PDCCH is called downlink control information (DCI). TheDCI includes UL resource allocation information, DL resource controlinformation, or a UL transmit (Tx) power control command for any UEgroup.

1.3. Dual Connectivity

FIG. 7 is a diagram for explaining the concept of dual connectivityapplicable to the present disclosure.

Referring to FIG. 7 , carrier aggregation may be performed between amacro cell 600 and small cells 610 and 620. That is, the macro cell mayuse n carriers (where n is a random positive integer), and the smallcell may use k carriers (where k is a random positive integer). In thiscase, the macro and small cells may use the same frequency carriers ordifferent frequency carriers. For example, the macro cell may use anyfrequencies F1 and F2, and the small cell may use any frequencies F2 andF3.

A random UE in the coverage of the small cell may be connected to themacro and small cells at the same time. Thus, the UE may be served bythe macro and small cells at the same time or through time divisionmultiplexing (TDM). Functions provided by the C-plane (e.g., connectionmanagement, mobility, etc.) may be served to the UE through a macro-celllayer. In the case of the U-plane data path, either or both of the macrocell and small cell may be selected. For example, in the case ofreal-time data such as Voice over LTE (VoLTE), the UE may performtransmission/reception with the macro cell capable of guaranteeinghigher mobility than the small cell. For a best-effect service, the UEmay be served by the small cell. The macro and small cells may beconnected through backhaul, and the backhaul may be ideal backhaul ornon-ideal backhaul.

The macro and small cells may be configured with the same system. Forexample, when one cell is configured with one of the FDD or TDD systems,the other cell may be configured with the same system. Alternatively,the macro and small cells may be configured with different systems. Forexample, one cell may be configured with the TDD system, and the othercell may be configured with the FDD system.

The concept of the dual connectivity has been described above withreference to FIG. 7 . The macro and small cells may use the samefrequency bands or different frequency bands. If a random UE isconfigured to operate in dual connectivity mode, the UE may be connectedto the macro and small cells at the same time. FIG. 7 shows a case inwhich the U-plane data path is set in the small cell.

Although the present disclosure describes that a random UE isdual-connected to macro and small cells for convenience of description,the disclosure is not limited to cell types (e.g., a macro cell, microcell, pico cell, femto cell, etc.). In addition, although the presentdisclosure describes that a random dual-connectivity UE configurescarrier aggregation (CA) by setting a macro cell to a primary cell(PCell) and a small cell to a secondary cell (SCell), the disclosure isnot limited thereto.

In particular, according to the present disclosure, a single UE may bedual-connected to an eNB (supporting an unlicensed band) in the LTEsystem and a transmission reception point (TRP) in the NR system.

2. NEW RADIO (NR) SYSTEM

As more and more communication devices require greater communicationcapacity, there is a need for mobile broadband communication enhancedover existing radio access technology (RAT). In addition, massivemachine-type communications (MTC) capable of providing a variety ofservices anywhere and anytime by connecting multiple devices and objectsis also considered. Communication system design considering services/UEssensitive to reliability and latency is also under discussion.

As a number of communication devices have required higher communicationcapacity, the necessity for the mobile broadband communication enhancedover the existing radio access technology (RAT) has increased. Inaddition, massive machine type communications (MTC) capable of providingvarious services anytime and anywhere by connecting a number of devicesor things to each other has also been considered. Moreover, acommunication system design capable of supporting services/UEs sensitiveto reliability and latency has been discussed. In the presentdisclosure, the corresponding technology is referred to as new RAT ornew radio (NR).

2.1. Numerologies

The NR system to which the present disclosure is applicable supportsvarious OFDM numerologies as shown in Table 2 below. The value of μ andcyclic prefix information per carrier bandwidth part may be signaled forDL and UL, respectively. For example, the value of μ and cyclic prefixinformation for a DL carrier bandwidth part may be signaled thoughhigher layer signaling such as DL-BWP-mu and DL-MWP-cp. As anotherexample, the value of μ and cyclic prefix information for a UL carrierbandwidth part may be signaled though higher layer signaling such asUL-BWP-mu and UL-MWP-cp.

TABLE 3 μ Δf = 2^(μ) · 15 [kHz] Cyclic prefix 0 15 Normal 1 30 Normal 260 Normal, Extended 3 120 Normal 4 240 Normal

2.2. Frame Structure

DL and UL transmission are configured with frames each having a durationof 10 ms. Each frame may include 10 subframes, each having a duration of1 ms. In this case, the number of consecutive OFDM symbols in eachsubframe is N_(symb) ^(subframeμ)=N_(symb) ^(slot) N_(slot)^(subframeμ).

Each frame may include two half-frames with the same size. In this case,the two half-frames may include subframes 0 to 4 and subframes 5 to 9,respectively.

Regarding the subcarrier spacing μ, slots in one subframe may benumbered in ascending order as follows: n_(s) ^(μ)∈{0, . . . , N_(slot)^(subframe,μ)−1}, and slots in one frame may be numbered in ascendingorder as follow: n_(s,f) ^(μ)∈{0, . . . , N_(slot) ^(frame,μ)−1}. Inthis case, the number of consecutive OFDM symbols in one slot (N_(symb)^(slot)) may be determined as shown in Tables 4 and 5 below according tothe CP. The start slot (n_(s) ^(μ)) in a subframe is aligned with thestart OFDM symbol (n_(s) ^(μ)N_(symb) ^(slot)) in the correspondingsubframe in the time domain. Table 3 shows the number of OFDM symbols ineach slot/frame/subframe in the case of a normal CP, and Table 4 showsthe number of OFDM symbols in each slot/frame/subframe in the case of anextended CP.

TABLE 4 μ N_(symb) ^(slot) N_(slot) ^(frame, μ) N_(slot) ^(subframe, μ)0 14 10 1 1 14 20 2 2 14 40 4 3 14 80 8 4 14 160 16 5 14 320 32

TABLE 5 μ N_(symb) ^(slot) N_(slot) ^(frame, μ) N_(slot) ^(subframe, μ)2 12 40 4

The NR system to which the present disclosure is applicable may employ aself-contained slot structure as the above-described slot structure.

FIG. 8 is a diagram illustrating a self-contained slot structureapplicable to the present disclosure.

In FIG. 8 , the hatched area (e.g., symbol index=0) indicates a DLcontrol region, and the black area (e.g., symbol index=13) indicates aUL control region. The remaining area (e.g., symbol index=1 to 12) maybe used for DL or UL data transmission.

Based on this structure, an eNB and a UE may sequentially perform DLtransmission and UL transmission in one slot. That is, the eNB and UEmay transmit and receive not only DL data but also a UL ACK/NACK for theDL data in one slot. Consequently, this structure may reduce a timerequired until data retransmission when a data transmission erroroccurs, thereby minimizing the latency of a final data transmission.

In this self-contained slot structure, a predetermined length of timegap is required to allow the eNB and UE to switch from transmission modeto reception mode and vice versa. To this end, in the self-containedslot structure, some OFDM symbols at the time of switching from DL to ULmay be configured as a GP.

Although it has been described above that the self-contained slotstructure includes both DL and UL control regions, these control regionsmay be selectively included in the self-contained slot structure. Inother words, the self-contained slot structure according to the presentdisclosure may include either the DL control region or the UL controlregion as well as both the DL and UL control regions as illustrated inFIG. 8 .

For example, a slot may have various slot formats. In this case, OFDMsymbols in each slot may be classified into a DL symbol (denoted by‘D’), a flexible symbol (denoted by ‘X’), and a UL symbol (denoted by‘U’).

Thus, a UE may assume that DL transmission occurs only in symbolsdenoted by ‘D’ and ‘X’ in a DL slot. Similarly, the UE may assume thatUL transmission occurs only in symbols denoted by ‘U’ and ‘X’ in a ULslot.

2.3. Analog Beamforming

In a millimeter wave (mmW) system, since a wavelength is shortened, aplurality of antenna elements may be installed in the same area. Thatis, considering that the wavelength at 30 GHz band is 1 cm, a total of100 antenna elements may be installed in a 5*5 cm panel at intervals of0.5 lambda (wavelength) in the case of a 2-dimensional array. Therefore,in the mmW system, it is possible to improve coverage or throughput byincreasing the beamforming (BF) gain using multiple antenna elements.

In this case, each antenna element may include a transceiver unit (TXRU)to enable adjustment of transmission power and phases per antennaelement. By doing so, each antenna element may perform independentbeamforming per frequency resource.

However, installing TXRUs in all of the about 100 antenna elements isless feasible in terms of cost. Therefore, a method of mapping aplurality of antenna elements to one TXRU and adjusting the direction ofa beam using an analog phase shifter has been considered. However, thismethod is disadvantageous in that frequency selective beamforming isimpossible because only one beam direction is generated over the fullband.

To solve this problem, as an intermediate form of digital BF and analogBF, hybrid BF with B TXRUs that are fewer than Q antenna elements may beconsidered. In the case of the hybrid BF, the number of beam directionsthat may be transmitted at the same time is limited to B or less, whichdepends on how B TXRUs and Q antenna elements are connected.

FIGS. 9 and 10 are diagrams illustrating representative methods forconnecting TXRUs to antenna elements. Here, the TXRU virtualizationmodel represents the relationship between TXRU output signals andantenna element output signals.

FIG. 9 shows a method for connecting TXRUs to sub-arrays. In FIG. 9 ,one antenna element is connected to one TXRU.

FIG. 10 shows a method for connecting all TXRUs to all antenna elements.In FIG. 10 , all antenna elements are connected to all TXRUs. In thiscase, extra addition units are required to connect all antenna elementsto all TXRUs as shown in FIG. 10 .

In FIGS. 9 and 10 , W indicates a phase vector weighted by an analogphase shifter. That is, W is a major parameter determining the directionof the analog beamforming. In this case, the mapping relationshipbetween CSI-RS antenna ports and TXRUs may be 1:1 or 1-to-many.

The configuration shown in FIG. 9 has a disadvantage in that it isdifficult to achieve beamforming focusing but has an advantage in thatall antennas can be configured at low cost.

On the contrary, the configuration shown in FIG. 10 is advantageous inthat beamforming focusing can be easily achieved. However, since allantenna elements are connected to the TXRU, it has a disadvantage ofhigh cost.

When a plurality of antennas is used in the NR system to which thepresent disclosure is applicable, a hybrid beamforming (BF) scheme inwhich digital BF and analog BF are combined may be applied. In thiscase, analog BF (or radio frequency (RF) BF) means an operation ofperforming precoding (or combining) at an RF stage. In hybrid BF, eachof a baseband stage and the RF stage perform precoding (or combining)and, therefore, performance approximating to digital BF can be achievedwhile reducing the number of RF chains and the number of adigital-to-analog (D/A) (or analog-to-digital (A/D)) converters.

For convenience of description, a hybrid BF structure may be representedby N transceiver units (TXRUs) and M physical antennas. In this case,digital BF for L data layers to be transmitted by a transmission end maybe represented by an N-by-L matrix. N converted digital signals obtainedthereafter are converted into analog signals via the TXRUs and thensubjected to analog BF, which is represented by an M-by-N matrix.

FIG. 11 is a diagram schematically illustrating an exemplary hybrid BFstructure from the perspective of TXRUs and physical antennas accordingto the present disclosure. In FIG. 11 , the number of digital beams is Land the number analog beams is N.

Additionally, in the NR system to which the present disclosure isapplicable, an BS designs analog BF to be changed in units of symbols toprovide more efficient BF support to a UE located in a specific area.Furthermore, as illustrated in FIG. 11 , when N specific TXRUs and M RFantennas are defined as one antenna panel, the NR system according tothe present disclosure considers introducing a plurality of antennapanels to which independent hybrid BF is applicable.

In the case in which the BS utilizes a plurality of analog beams asdescribed above, the analog beams advantageous for signal reception maydiffer according to a UE. Therefore, in the NR system to which thepresent disclosure is applicable, a beam sweeping operation is beingconsidered in which the BS transmits signals (at least synchronizationsignals, system information, paging, and the like) by applying differentanalog beams in a specific subframe (SF) or slot on a symbol-by-symbolbasis so that all UEs may have reception opportunities.

FIG. 12 is a diagram schematically illustrating an exemplary beamsweeping operation for a synchronization signal and system informationin a DL transmission procedure according to the present disclosure.

In FIG. 12 below, a physical resource (or physical channel) on which thesystem information of the NR system to which the present disclosure isapplicable is transmitted in a broadcasting manner is referred to as anxPBCH. Here, analog beams belonging to different antenna panels withinone symbol may be simultaneously transmitted.

As illustrated in FIG. 12 , in order to measure a channel for eachanalog beam in the NR system to which the present disclosure isapplicable, introducing a beam RS (BRS), which is a reference signal(RS) transmitted by applying a single analog beam (corresponding to aspecific antenna panel), is being discussed. The BRS may be defined fora plurality of antenna ports and each antenna port of the BRS maycorrespond to a single analog beam. In this case, unlike the BRS, asynchronization signal or the xPBCH may be transmitted by applying allanalog beams in an analog beam group such that any UE may receive thesignal well.

2.4. Synchronization Signal Block (SSB) or SS/PBCH Block

In the NR system to which the present disclosure is applicable, aprimary synchronization signal (PSS), a secondary synchronization signal(SSS), and/or a physical broadcast signal (PBCH) may be transmitted inone SS block or SS PBCH block (hereinafter, referred to as an SSB orSS/PBCH block). Multiplexing other signals may not be precluded withinthe SSB.

The SS/PBCH block may be transmitted in a band other than the center ofa system band. Particularly, when the BS supports broadband operation,the BS may transmit multiple SS/PBCH blocks.

FIG. 13 is a schematic diagram illustrating an SS/PBCH block applicableto the present disclosure.

As illustrated in FIG. 13 , the SS/PBCH block applicable to the presentdisclosure may include 20 RBs in four consecutive OFDM symbols.

Further, the SS/PBCH block may be transmitted even in a frequency bandother than the center frequency of a frequency band used by the network.

For this purpose, a synchronization raster being candidate frequencypositions at which the UE should detect the SS/PBCH block is defined inthe NR system to which the present disclosure is applicable. Thesynchronization raster may be distinguished from a channel raster.

In the absence of explicit signaling of the position of the SS/PBCHblock, the synchronization raster may indicate available frequencypositions for the SS/PBCH block, at which the UE may acquire systeminformation.

The synchronization raster may be determined based on a globalsynchronization channel number (GSCN). The GSCN may be transmitted byRRC signaling (e.g., an MIB, a system information block (SIB), remainingminimum system information (RMSI), other system information (OSI), orthe like).

The synchronization raster is defined to be longer along the frequencyaxis than the channel raster and characterized by a smaller number ofblind detections than the channel raster, in consideration of thecomplexity of initial synchronization and a detection speed.

FIG. 14 is a schematic diagram illustrating an SS/PBCH blocktransmission structure applicable to the present disclosure.

In the NR system to which the present disclosure is applicable, the BSmay transmit an SS/PBCH block up to 64 times for 5 ms. The multipleSS/PBCH blocks may be transmitted on different beams, and the UE maydetect the SS/PBCH block on the assumption that the SS/PBCH block istransmitted on a specific one beam every 20 ms.

As the frequency band is higher, the BS may set a larger maximum numberof beams available for SS/PBCH block transmission within 5 ms. Forexample, the BS may transmit the SS/PBCH block by using up to 4different beams at or below 3 GHz, up to 8 different beams at 3 to 6GHz, and up to 64 different beams at or above 6 GHz, for 5 ms.

2.5. Synchronization Procedure

The UE may acquire synchronization by receiving the above-describedSS/PBCH block from the BS. The synchronization procedure largelyincludes cell ID detection and timing detection. The cell ID detectionmay include PSS-based cell ID detection and SSS-based cell ID detection.The timing detection may include PBCH DMRS-based timing detection andPBCH contents-based (e.g., MIB-based) timing detection.

First, the UE may acquire timing synchronization and the physical cellID of a detected cell by detecting a PSS and an SSS. More specifically,the UE may acquire the symbol timing of the SS block and detect a cellID within a cell ID group, by PSS detection. Subsequently, the UEdetects the cell ID group by SSS detection.

Further, the UE may detect the time index (e.g., slot boundary) of theSS block by the DMRS of the PBCH. The UE may then acquire half-frameboundary information and system frame number (SFN) information from anMIB included in the PBCH.

The PBCH may indicate that a related (or corresponding) RMSI PDCCH/PDSCHis transmitted in the same band as or a different band from that of theSS/PBCH block. Accordingly, the UE may then receive RMSI in a frequencyband indicated by the PBCH or a frequency band carrying the PBCH, afterdecoding of the PBCH.

2.6. Quasi Co-located or Quasi Co-location (QCL)

In the present disclosure, QCL may mean one of the following.

(1) If two antenna ports are “quasi co-located (QCL)”, the UE may assumethat large-scale properties of a signal received from a first antennaport may be inferred from a signal received from the other antenna port.The “large-scale properties” may include one or more of the following.

-   -   Delay spread    -   Doppler spread    -   Frequency shift    -   Average received power    -   Received Timing

(2) If two antenna ports are “quasi co-located (QCL)”, the UE may assumethat large-scale properties of a channel over which a symbol on oneantenna port is conveyed may be inferred from a channel over which asymbol on the other antenna port is conveyed). The “large-scaleproperties” may include one or more of the following.

-   -   Delay spread    -   Doppler spread    -   Doppler shift    -   Average gain    -   Average delay    -   Average angle (AA): When it is said that QCL is guaranteed        between antenna ports in terms of AA, this may imply that when a        signal is to be received from other antenna port(s) based on an        AA estimated from specific antenna port(s), the same or similar        reception beam direction (and/or reception beam width/sweeping        degree) may be set and the reception is processed accordingly        (in other words, that when operated in this manner, reception        performance at or above a certain level is guaranteed).    -   Angular spread (AS): When it is said that QCL is guaranteed        between antenna ports in terms of AS, this may imply that an AS        estimated from one antenna port may be derived/estimated/applied        from an AS estimated from another antenna port.    -   Power Angle(-of-Arrival) Profile (PAP): When it is said that QCL        is guaranteed between antenna ports in terms of PAP, this may        imply that a PAP estimated from one antenna port may be        derived/estimated/applied from a PAP estimated from another        antenna port (or the PAPs may be treated as similar or        identical).

In the present disclosure, both of the concepts defined in (1) and (2)described above may be applied to QCL. Alternatively, the QCL conceptsmay be modified such that it may be assumed that signals are transmittedfrom a co-location, for signal transmission from antenna ports for whichthe QCL assumption is established (e.g., the UE may assume that theantenna ports are transmitted from the same transmission point).

In the present disclosure, partial QCL between two antenna ports maymean that at least one of the foregoing QCL parameters for one antennaport is assumed/applied/used as the same as for the other antenna port(when an associated operation is applied, performance at or above acertain level is guaranteed).

2.7. Bandwidth Part (BWP)

In the NR system to which the present disclosure is applicable,frequency resources of up to 400 MHz per component carrier (CC) may beallocated/supported. When a UE operating in such a wideband CC alwaysoperates with a radio frequency (RF) module for the entire CCs turnedon, battery consumption of the UE may increase.

Alternatively, considering various use cases (e.g., enhanced mobilebroadband (eMBB), ultra-reliable and low latency communication (URLLC),and massive machine type communication (mMTC), and so on) operatingwithin a single wideband CC, a different numerology (e.g., SCS) may besupported for each frequency band within the CC.

Alternatively, the maximum bandwidth capability may be different foreach UE.

In consideration of the above situation, the BS may indicate/configurethe UE to operate only in a partial bandwidth instead of the entirebandwidth of the wideband CC. The partial bandwidth may be defined as aBWP.

A BWP may include contiguous RBs on the frequency axis, and one BWP maycorrespond to one numerology (e.g., SCS, CP length, slot/mini-slotduration, and so on).

The BS may configure a plurality of BWPs in one CC configured for theUE. For example, the BS may configure a BWP occupying a relatively smallfrequency area in a PDCCH monitoring slot, and schedule a PDSCHindicated by the PDCCH (or a PDSCH scheduled by the PDCCH) in a largerBWP. Alternatively, when UEs are concentrated on a specific BWP, the BSmay configure another BWP for some of the UEs, for load balancing.Alternatively, the BS may exclude some spectrum of the entire bandwidthand configure both of the BWPs in the same slot in consideration offrequency-domain inter-cell interference cancellation betweenneighboring cells.

The BS may configure at least one DL/UL BWP for a UE associated with thewideband CC, and activate at least one of DL/UL BWPs configured at aspecific time point (by L1 signaling (e.g., DCI or the like), MACsignaling, RRC signaling, or the like). The activated DL/UL BWP may bereferred to as an active DL/UL BWP. During initial access or before anRRC connection setup, the UE may not receive a configuration for a DL/ULBWP from the BS. A DL/UL BWP assumed for the UE is defined as an initialactive DL/UL BWP.

3. UNLICENSED BAND SYSTEM

FIGS. 15A and 15B illustrate an exemplary wireless communication systemsupporting an unlicensed band, which is applicable to the presentdisclosure.

In the following description, a cell operating in a licensed band(hereinafter, referred to as L-band) is defined as an L-cell, and acarrier of the L-cell is defined as a (DL/UL) LCC. In addition, a celloperating in an unlicensed band (hereinafter, referred to as a U-band)is defined as a U-cell, and a carrier of the U-cell is defined as a(DL/UL) UCC. The carrier/carrier-frequency of the cell may refer to theoperating frequency (e.g., center frequency) of the cell. A cell/carrier(e.g., CC) is collectively referred to as a cell.

As illustrated in FIG. 15A, when the UE and the BS transmit and receivesignals in carrier-aggregated LCC and UCC, the LCC may be configured asa primary CC (PCC) and the UCC may be configured as a secondary CC(SCC).

As illustrated in FIG. 15B, the UE and the BS may transmit and receivesignals in one UCC or a plurality of carrier-aggregated LCC and UCC.That is, the UE and the BS may transmit and receive signals only in theUCC(s) without the LCC.

The above-described operation of transmitting and receiving a signal ina U-band according to the present disclosure may be performed based onall the deployment scenarios described above (unless otherwise stated).

3.1. Radio Frame Structure for Unlicensed Band

For operation in U-bands, LTE frame structure type 3 (see FIG. 3 ) orthe NR frame structure (see FIG. 8 ) may be used. The configuration ofOFDM symbols reserved for UL/DL signal transmission in a frame structurefor U-bands may be determined by a BS. In this case, the OFDM symbol maybe replaced with an SC-FDM(A) symbol.

To transmit a DL signal in a U-band, the BS may inform a UE of theconfiguration of OFDM symbols used in subframe #n through signaling.Herein, a subframe may be replaced with a slot or a time unit (TU).

Specifically, in the LTE system supporting U-bands, the UE may assume(or recognize) the configuration of occupied OFDM symbols in subframe #nbased on a specific filed in DCI (e.g., Subframe configuration for LAA′field, etc.), which is received in subframe #n−1 or subframe #n from theBS.

Table 6 shows how the Subframe configuration for LAA field indicates theconfiguration of OFDM symbols used to transmit DL physical channelsand/or physical signals in the current or next subframe.

TABLE 6 Value of Configuration of ‘Subframe configuration occupied OFDMfor LAA’ symbols (current field in current subframe subframe, nextsubframe) 0000 (—, 14) 0001 (—, 12) 0010 (—, 11) 0011 (—, 10) 0100 (—,9)  0101 (—, 6)  0110 (—, 3)  0111 (14, *)  1000 (12, —) 1001 (11, —)1010 (10, —) 1011  (9, —) 1100  (6, —) 1101  (3, —) 1110 reserved 1111reserved NOTE: (—, Y) means UE may assume the first Y symbols areoccupied in next subframe and other symbols in the next subframe are notoccupied. (X, —) means UE may assume the first X symbols are occupied incurrent subframe and other symbols in the current subframe are notoccupied. (X, *) means UE may assume the first X symbols are occupied incurrent subframe, and at least the first OFDM symbol of the nextsubframe is not occupied.

To transmit a UL signal in a U-band, the BS may provide information on aUL transmission interval to the UE through signaling.

Specifically, in the LTE system supporting U-bands, the UE may obtain‘UL duration’ and ‘UL offset’ information for subframe #n from the ‘ULduration and offset’ field in detected DCI.

Table 7 shows how the UL duration and offset field indicates theconfigurations of a UL offset and a UL duration.

TABLE 7 Value of ‘UL duration UL offset, l UL duration, d and offset’field (in subframes) (in subframes) 00000 Not configured Not configured00001 1 1 00010 1 2 00011 1 3 00100 1 4 00101 1 5 00110 1 6 00111 2 101000 2 2 01001 2 3 01010 2 4 01011 2 5 01100 2 6 01101 3 1 01110 3 201111 3 3 10000 3 4 1000l 3 5 10010 3 6 10011 4 1 10100 4 2 10101 4 310110 4 4 10111 4 5 11000 4 6 11001 6 1 11010 6 2 11011 6 3 11100 6 411101 6 5 11110 6 6 11111 reserved reserved

For example, when the UL duration and offset field configures (orindicates) a UL offset 1 and a UL duration d for subframe #n, the UE maynot need to receive DL physical channels and/or physical signals insubframe #n+1+i (where i=0, 1, . . . , d−1).

3.2. DL Channel Access Procedure (DL CAP)

For a DL signal transmission in the U-band, the BS may perform a DL CAPfor the U-band. On the assumption that the BS is configured with a PCellthat is a licensed band and one or more SCells which are U-bands, a DLCAP operation applicable to the present disclosure will be describedbelow in detail, with the U-bands represented as licensed assistedaccess (LAA) SCells. The DL CAP operation may be applied in the samemanner even when only a U-band is configured for the BS.

3.2.1. Channel Access Procedure for Transmission(s) IncludingPDSCH/PDCCH/EPDCCH

The BS senses whether a channel is in an idle state for a slot durationof a defer duration T_(d). After a counter N is decremented to 0 in step4 as described later, the BS may perform a transmission including aPDSCH/PDCCH/EPDCCH on a carrier on which the next LAA SCell(s)transmission is performed. The counter N may be adjusted by sensing thechannel for an additional slot duration according to the followingprocedure.

1) Set N=N_(init) where N_(init) is a random number uniformlydistributed between 0 and CW_(p), and go to step 4.

2) If N>0 and the BS chooses to reduce the counter, set N=N−1.

3) Sense the channel for an additional slot duration, and if theadditional slot duration is idle, go to step 4. Else, go to step 5.

4) If N=0, stop. Else, go to step 2.

5) Sense the channel until a busy slot is detected within the additionaldefer duration T_(d) or all slots of the additional defer duration T_(d)are sensed as idle.

6) If the channel is sensed as idle for all slot durations of theadditional defer duration Et, go to step 4. Else, go to step 5.

The above-described CAP for a transmission including aPDSCH/PDCCH/EPDCCH of the BS may be summarized as follows.

FIG. 16 is a flowchart illustrating a CAP for transmission in a U-band,which is applicable to the present disclosure.

For a DL transmission, a transmission node (e.g., a BS) may initiate theCAP to operate in LAA SCell(s) which is U-band cell(s) (S1610).

The BS may randomly select a backoff counter N within a contentionwindow (CW) according to step 1. N is set to an initial value, N_(init)(S1620). N_(init) is a random value selected from among the valuesbetween 0 and CW_(p).

Subsequently, if the backoff counter N is 0 in step 4 (Y in S1630), theBS terminates the CAP (S1632). Subsequently, the BS may perform a Txburst transmission including a PDSCH/PDCCH/EPDCCH (S1634). On the otherhand, if the backoff counter N is not 0 (N in S1630), the BS decrementsthe backoff counter N by 1 according to step 2 (S1640).

Subsequently, the BS determines whether the channel of the LAA SCell(s)is in an idle state (S1650). If the channel is in the idle state (YinS1650), the BS determines whether the backoff counter N is 0 (S1630).

On the contrary, if the channel is not idle in step S1650, that is, thechannel is busy (N in S1650), the BS determines whether the channel isin the idle state for a defer duration T_(d) (25 usec or more) longerthan a slot time (e.g., 9 usec) according to step 5 (S1660). If thechannel is idle for the defer duration (Y in S1670), the BS may resumethe CAP.

For example, if the backoff counter N_(init) is 10 and then reduced to5, and the channel is determined to be busy, the BS senses the channelfor the defer duration and determines whether the channel is idle. Ifthe channel is idle for the defer duration, the BS may resume the CAPfrom a backoff counter value 5 (or from a backoff counter value 4 afterdecrementing the backoff counter value by 1).

On the other hand, if the channel is busy for the defer duration (N inS1670), the BS re-performs step S1660 to check again whether the channelis idle for a new defer duration.

In the above procedure, if the BS does not perform the transmissionincluding the PDSCH/PDCCH/EPDCCH on the carrier on which a LAA SCell(s)transmission is performed after step 4, the BS may perform thetransmission including the PDSCH/PDCCH/EPDCCH on the carrier, when thefollowing conditions are satisfied:

When the BS is prepared to transmit the PDSCH/PDCCH/EPDCCH and thechannel is sensed as idle for at least a slot duration T_(sl), or forall slot durations of the defer duration T_(d) immediately before thetransmission; and

On the contrary, when the BS does not sense the channel as idle for theslot duration T_(sl) or for any of the slot durations of the deferduration T_(d) immediately before the intended transmission, the BSproceeds to step 1 after sensing the channel as idle for a slot durationof the defer duration T_(d).

The defer duration T_(d) includes a duration of T_(f) (=16 us)immediately followed by m_(p) consecutive slot durations where each slotduration T_(sl) is 9 us, and T_(f) includes an idle slot duration T_(sl)at the start of T_(f).

If the BS senses the channel for the slot duration T_(sl) and powerdetected by the BS for at least 4 us within the slot duration is lessthan an energy detection threshold X_(Thresh), the slot duration T_(sl)is considered to be idle. Otherwise, the slot duration T_(sl) isconsidered to be busy.

CW_(min,p)≤CW_(p)≤CW_(max,p) represents a contention window. CW_(p)adjustment will be described in section 3.2.3.

CW_(min),p and CW_(max,p) are chosen before step 1 of the aboveprocedure.

m_(p), CW_(min,p), and CW_(max,p) are based on a channel access priorityclass associated with the transmission of the BS (see Table 13 below).

X_(Thresh) is adjusted according to section 3.2.4.

TABLE 8 Channel Access Priority Class allowed (p) m_(p) CW_(min, p)CW_(max, p) T_(mcot, p) CW_(p) sizes 1 1 3 7 2 ms {3, 7} 2 1 7 15 3 ms{7, 15} 3 3 15 63 8 or {15, 31, 63} 10 ms 4 7 15 1023 8 or {15, 31, 63,127, 10 ms 255, 511, 1023}

If the BS performs a discovery signal transmission which does notinclude a PDSCH/PDCCH/EPDCCH when N>0 in the above procedure, the BSdoes not decrement N for a slot duration overlapping with the discoverysignal transmission.

The BS does not continuously perform transmissions on the channel, for aperiod exceeding T_(mcot,p) as given in Table 13 on the carrier on whichan LASS SCell transmission is performed.

For p=3 and p=4 in Table 8, if the absence of any other technologysharing the carrier may be guaranteed on a long term basis (e.g., bylevel of regulation), T_(mcpt,p)=10 ms and otherwise, T_(mcot,p)=8 ms.

3.2.2. Channel Access Procedure for Transmissions Including DiscoverySignal Transmission(S) and Not Including PDSCH

If the transmission duration of the BS is 1 ms or less, the BS mayperform a transmission including a discovery signal transmission withouta PDSCH on a carrier on which a LAA SCell transmission is performed,immediately after a corresponding channel is sensed as idle for at leasta sensing interval T_(drs) (25 us). T_(drs) includes a duration of T_(f)(=16 us) immediately followed by one slot duration T_(sl) (=9 us). T_(f)includes an idle slot duration T_(sl) at the start of T_(f). If thechannel is sensed as idle for the slot duration T_(drs), the channel isconsidered to be idle for Tars.

3.2.3. Contention Window Adjustment Procedure

If the BS performs a transmission including a PDSCH associated with achannel access priority class p on a carrier, the BS maintains andadjusts a contention window value CW_(p) by using the followingprocedures before step 1 of the procedure described in section 2.2.1.for the transmission (i.e., before performing a CAP):

1> Set CW_(p)=CW_(min,p) for all priority classes p∈{1,2,3,4}.

2> If at least 80% (z=80%) of HARQ-ACK values corresponding to PDSCHtransmission(s) in a reference subframe k are determined to be NACK, theBS increments CW_(p) for all priority classes p∈{1,2,3,4} to the nexthigher allowed value and remains in step 2. Otherwise, the BS goes tostep 1.

In other words, when the probability that the HARQ-ACK valuescorresponding to the PDSCH transmission(s) in reference subframe k aredetermined to be NACK is at least 80%, the BS increments a CW value setfor each priority class to the next higher value. Alternatively, the BSmaintains the CW value set for each priority class to be an initialvalue.

Reference subframe k is the starting subframe of the most recenttransmission on the carrier made by the BS, for which at least someHARQ-ACK feedback is expected to be available.

The BS adjusts the CW_(p) values for all priority classes p∈{1,2,3,4}only once based on the given reference subframe k.

If CW_(p)=CW_(max,p), the next higher allowed value for the CW_(p)adjustment is CW_(max,p).

The probability Z of determining HARQ-ACK values corresponding to PDSCHtransmission(s) in reference subframe k to be NACK may be determined inconsideration of the following.

-   -   If the transmission(s) of the BS for which HARQ-ACK feedback is        available starts in the second slot of subframe k, HARQ-ACK        values corresponding to PDSCH transmission(s) in subframe k and        additionally, HARQ-ACK values corresponding to PDSCH        transmission(s) in subframe k+1 are used.    -   If HARQ-ACK values correspond to PDSCH transmission(s) in the        same LAA SCell allocated by an (E)PDCCH transmitted in LAA        SCell,    -   If an HARQ-ACK feedback for a PDSCH transmission of the BS is        not detected or if the BS detects a ‘DTX’, ‘NACK/DTX’ or (any)        other state, it is counted as NACK.    -   If the HARQ-ACK values correspond to PDSCH transmission(s) in        another LAA SCell allocated by an (E)PDCCH transmitted in the        LAA SCell,    -   If an HARQ-ACK feedback for a PDSCH transmission of the BS is        detected, ‘NACK/DTX’ or (any) other state is counted as NACK and        the ‘DTX’ state is ignored.    -   If an HARQ-ACK feedback for a PDSCH transmission of the BS is        not detected,    -   If it is expected that the BS will use PUCCH format 1 with        channel selection, the ‘NACK/DTX’ state corresponding to ‘no        transmission’ is counted as NACK, and the ‘DTX’ state        corresponding to ‘no transmission’ is ignored. Otherwise, the        HARQ-ACK for the PDSCH transmission is ignored.    -   If the PDSCH transmission has two codewords, an HARQ-ACK value        for each codeword is considered individually.    -   A bundled HARQ-ACK across M subframes is considered to be M        HARQ-ACK responses.

If the BS performs a transmission which includes a PDCCH/EPDDCH with DCIformat 0A/0B/4A/4B and does not include a PDSCH associated with thechannel access priority class p on a channel starting from time to, theBS maintains and adjusts the competing window size CW_(p) by using thefollowing procedures before step 1 of the procedure described in section3.2.1. for the transmission (i.e., before performing the CAP):

1> Set CW_(p)=CW_(min,p) for all priority classes p∈{1,2,3,4}.

2> If a UE using a type 2 CAP (described in section 2.3.1.2.)successfully receives less than 10% of UL transport blocks (TBs)scheduled by the BS during a time period t₀ and t₀+T_(CO), the BSincrements CW_(p) for all priority classes to the next higher allowedvalue and remains in step 2. Otherwise, the BS goes to step 1.

T_(CO) is calculated according to section 3.3.1.

If CW_(p)=CW_(max,p) is used K times consecutively to generate N_(init),only CW_(p) for a priority class p for CW_(p)=CW_(max,p) used K timesconsecutively to generate N_(init) is reset to CW_(min,p). the BS thenselects K from a set of {1, 2, . . . , 8} values for each priority classp∈{1,2,3,4}.

3.2.4. Energy Detection Threshold Adaptation Procedure

A BS accessing a carrier on which a LAA SCell transmission is performedsets an energy detection threshold X_(Thresh) to a maximum energydetection threshold X_(Thresh_max) or less.

The maximum energy detection threshold X_(Thresh_max) is determined asfollows.

-   -   If the absence of any other technology sharing the carrier may        be guaranteed on a long term basis (e.g., by level of        regulation),

$X_{T{hresh\_ ma}x} = {\min\begin{Bmatrix}{{T_{\max} + {10{dB}}},} \\X_{r}\end{Bmatrix}}$

-   -   where X_(r) is the maximum energy detection threshold (in dBm)        defined in regulatory requirements, when the regulation is        defined. Otherwise, X_(r)=T_(max)+10 dB.    -   Else,

$X_{T{hres\_ ma}x} = {\max\begin{Bmatrix}{{{- 72} + {{10 \cdot \log}10\left( {{BW}{MHz}/20{MHz}} \right){dBm}}},} \\{\min\begin{Bmatrix}{T_{\max},} \\{T_{\max} - T_{a} + \left( {P_{H} + {{10 \cdot \log}10\left( {{BW}{MHz}/20{MHz}} \right)} - P_{TX}} \right.}\end{Bmatrix}}\end{Bmatrix}}$

-   -   Herein, each variable is defined as follows.    -   T_(A)=10 dB for transmission(s) including PDSCH;    -   T_(A)=5 dB for transmissions including, discovery signal        transmissions) and not including PDSCH;    -   P_(H)=23 dBm;    -   P_(TX) is the set maximum eNB output power in dBm for the        carrier;        -   eNB uses the set maximum transmission power over a single            carrier irrespective of whether single carrier or            multi-carrier transmission is employed            T _(max) (dBm)=10·log 10(3.16228·10⁻⁸(mW/MHz)·BWMHz(MHz));    -   BWMHz is the single carrier bandwidth in MHz.

3.2.5. Channel Access Procedure for Transmission(S) on Multiple Carriers

The BS may access multiple carriers on which a LAA SCell transmission isperformed in one of the following type A or type B procedures.

3.2.5.1. Type A Multi-Carrier Access Procedures

According to the procedure described in this section, the BS performschannel access on each carrier c_(i)∈C where C is a set of intendedcarriers to be transmitted by the BS, i=0, 1, . . . q−1, and q is thenumber of carriers to be transmitted by the BS.

The counter N described in section 3.2.1 (i.e., the counter N consideredin the CAP) is determined for each carrier c_(i), and in this case, thecounter for each carrier is represented as N_(c) _(i) ·N_(c) _(i) , ismaintained according to section 3.2.5.1.1. or section 3.2.5.1.2.

3.2.5.1.1. Type A1

The counter N described in section 3.2.1 (i.e., the counter N consideredin the CAP) is determined for each carrier c_(i), and the counter foreach carrier is represented as N_(c) _(i) .

In the case where the BS ceases a transmission on one carrier c_(j)∈C,if the absence of any other technology sharing the carrier may beguaranteed on a long term basis (e.g., by level of regulation), the BSmay resume N_(c) _(i) reduction, when an idle slot is detected afterwaiting for a duration of 4·T_(sl) or reinitializing N_(c) _(i) , foreach carrier c_(i) (where c_(i) is different from c_(j), c_(i)≠c_(j)).

3.2.5.1.2. Type A2

The counter N for each carrier c_(j)∈C may be determined according tosection 2.2.1., and is denoted by N_(c) _(j) . Here, c_(j) may mean acarrier having the largest CW_(p) value. For each carrier c_(j), N_(c)_(i) =N_(c) _(j) .

When the BS ceases a transmission on any one carrier for which N_(c)_(i) has been determined by the BS, the BS reinitializes N_(c) _(i) forall carriers.

3.2.5.2. Type B Multi-Carrier Access Procedure

A carrier c_(j)∈C may be selected by the BS as follows.

-   -   The BS selects c_(j) uniformly randomly from C before each        transmission on multiple carriers c_(i)∈C, or    -   The BS does not select c_(j) more than once every one second.

Herein, C is a set of carriers to be transmitted by the BS, i=0, 1, . .. q−1, and q is the number of carriers to be transmitted by the BS.

For a transmission on a carrier c_(j), the BS performs channel access onthe carrier c_(j) according to the procedure described in section 3.2.1along with the modification described in section 3.2.5.2.1 or section3.2.5.2.2.

For a transmission on the carrier c_(i)≠c_(j) among the carriersc_(i)∈C,

For each carrier c_(i), the BS senses the carrier c_(i) for at least asensing interval T_(mc)=25 us immediately before the transmission on thecarrier c_(i). The BS may perform a transmission on the carrier c_(i)immediately after sensing that the carrier c_(i) is idle for at leastthe sensing interval T_(mc). When the channel is sensed as idle duringall time periods in which idle sensing is performed on the carrier c_(j)within the given period T_(mc), the carrier c_(i) may be considered tobe idle for T_(mc).

The BS does not continuously perform transmissions on the carrierc_(i)≠c_(j) (c_(i)∈C) for a period exceeding T_(mcot,p) as given inTable 6. T_(mcot,p) is determined using the channel access parameterused for the carrier c_(j).

3.2.5.2.1. Type B1

A single CW_(p) value is maintained for the carrier set C.

To determine CW_(p) for channel access on a carrier c_(j), step 2 in theprocedure described in section 3.2.3. is modified as follows.

-   -   If at least 80% (Z=80%) of HARQ-ACK values corresponding to        PDSCH transmission(s) in reference subframe k of all carriers        c_(i)∈C are determined to be NACK, then CW_(p) for all priority        classes p∈{1,2, 3, 4} is incremented to the next higher allowed        value. Otherwise, the procedure goes to step 1.

3.2.5.2.2. Type B2 (Type B2)

The CW_(p) value is maintained independently for each carrier c_(j)∈C byusing the procedure described in section 3.2.3. To determine N_(init)for the carrier c_(j), the CW_(p) value of the carrier c_(j)∈C is used.Here, c_(j1) is a carrier having the largest CW_(j) among all carriersin the set C.

3.3. Uplink Channel Access Procedures

The UE and the BS that schedules a UL transmission for the UE performthe following procedure for access to a channel in which LAA SCelltransmission(s) is performed. On the assumption that the UE and the BSare basically configured with a PCell that is a licensed band and one ormore SCells which are U-bands, a UL CAP operation applicable to thepresent disclosure will be described below in detail, with the U-bandsrepresented as LAA SCells. The UL CAP operation may be applied in thesame manner even when only a U-band is configured for the UE and the BS.

3.3.1. Channel Access Procedure for Uplink Transmission(s)

The UE may access a carrier on which LAA SCell UL transmission(s) areperformed according to a type 1 or type 2 UL CAP. The type 1 CAP isdescribed in section 3.3.1.1, and the type 2 CAP is described in section3.3.1.2.

If a UL grant that schedules a PUSCH transmission indicates the type 1CAP, the UE performs type 1 channel access to perform a transmissionincluding the PUSCH transmission, unless otherwise stated in thissection.

If the UL grant that schedules the PUSCH transmission indicates the type2 CAP, the UE performs type 2 channel access to perform a transmissionincluding the PUSCH transmission, unless otherwise stated in thissection.

The UE performs type 1 channel access for an SRS transmission that doesnot include a PUSCH transmission. A UL channel access priority class p=1is used for the SRS transmission that does not include a PUSCH.

TABLE 9 Channel Access Priority allowed Class (p) m_(p) CW_(min, p)CW_(max, p) T_(ulmcot, p) CW_(p) sizes 1 2 3 7 2 ms {3, 7} 2 2 7 15 4 ms{7, 15} 3 3 15 1023 6 ms or {15, 31, 63, 127, 10 ms 255, 511, 1023} 4 715 1023 6 ms or {15, 31, 63, 127, 10 ms 255, 511, 1023} NOTE1: For p =3, 4, T_(ulmcot, p) = 10 ms if the higher layer parameter‘absenceOfAnyOtherTechnology-r14’ indicates TRUE, otherwise,T_(ulmcot, p) = 6 ms. NOTE 2: When T_(ulmcot, p) = 6 ms it may beincreased to 8 ms by inserting one or more gaps. The minimum duration ofa gap shall be 100 μs. The maximum duration before including any suchgap shall be 6 ms.

When the ‘UL configuration for LAA’ field configures ‘UL offset’ 1 and‘UL duration’ d for subframe n,

If the end of a UE transmission occurs in or before subframe n+1+d−1,the UE may use the type 2 CAP for transmission in subframe n+1+i (wherei=0, 1 . . . d−1).

If the UE is scheduled to perform a transmission including a PUSCH in asubframe set n₀, n₁, . . . n_(w−1) by using PDCCH DCI format 0B/4B, andthe UE may not perform channel access for transmission in subframen_(k), the UE should attempt to make a transmission in subframe n_(k+1)according to a channel access type indicated by DCI. k∈{0, 1, . . . w−2}and w is the number of scheduled subframes indicated by the DCI.

If the UE is scheduled to perform a transmission including a PUSCHwithout gaps in the subframe set n₀, n₁, . . . n_(w−1) by using one ormore of PDCCH DCI formats 0A/0B/4A/4B, and performs a transmission insubframe n_(k) after accessing a carrier according to the type 1 or type2 CAP, the UE may continue the transmission in a subframe after n_(k)where k∈{0, 1, . . . w−1}.

If the start of the UE transmission in subframe n+1 immediately followsthe end of the UE transmission in subframe n, the UE does not expectthat a different channel access type will be indicated for thetransmission in the subframe.

If the UE is scheduled to perform a transmission without gaps by usingone or more of PDCCH DCI formats 0A/0B/4A/4B, stops the transmissionduring or before subframe n_(k1) (where k1 ∈{0, 1, . . . w−2}), andcontinuously senses the corresponding channel as idle after stopping thetransmission, the UE may perform the transmission in the type 2 CAPafter subframe n_(k2) (where k2∈{1, . . . w−1}). If the channel is notsensed continuously as idle by the UE after the UE stops thetransmission, the UE may perform the transmission in the type 1 CAP of aUL channel access priority class indicated by DCI corresponding tosubframe n_(k2) after subframe n_(k2) (where k2∈{1, . . . w−1}).

If the UE receives a UL grant, DCI indicates the UE to start a PUSCHtransmission in subframe n by using the type 1 CAP, and the UE has anongoing type 1 CAP before subframe n,

-   -   If a UL channel access priority class value p1 used for the        ongoing type 1 CAP is equal to or greater than a UL channel        access priority class value p2 indicated by the DCI, the UE may        perform the PUSCH transmission by accessing a carrier in the        ongoing type 1 CAP.    -   If the UL channel access priority class value p1 used for the        ongoing type 1 CAP is less than the UL channel access priority        class value p2 indicated by the DCI, the UE terminates the        ongoing type 1 CAP.

If the UE is scheduled to transmit on a carrier set C in subframe n, aUL grant scheduling a PUSCH transmission on the carrier set C indicatesthe type 1 CAP, the same ‘PUSCH starting position’ is indicated for allcarriers of the carrier set C, and the carrier frequencies of thecarrier set C are a subset of a preset carrier frequency set,

-   -   The UE may perform a transmission on a carrier c_(i)∈C in the        type 2 CAP.    -   If the type 2 CAP has been performed on the carrier c_(i)        immediately before the UE transmission on a carrier c_(j)∈ C,        and    -   If the UE has accessed the carrier c_(j) by using the type 1        CAP,    -   Before performing the type 1 CAP on any one carrier in the        carrier set C, the UE uniformly randomly selects the carrier        c_(j) from the carrier set C.

When the BS has transmitted on the carrier according to the CAPdescribed in section 3.2.1, the BS may indicate the type 2 CAP by DCI ina UL grant that schedules a transmission including a PUSCH on thecarrier in subframe n.

Alternatively, when the BS has transmitted on the carrier according tothe CAP described in section 3.2.1, the BS may indicate that the type 2CAP is available for the transmission including the PUSCH on the carrierin subframe n by the ‘UL Configuration for LAA’ field.

Alternatively, when subframe n occurs within a time period starting fromto and ending at t₀+T_(CO), the BS may schedule the transmissionincluding the PUSCH on the carrier within subframe n following atransmission of a duration T_(short_ul)=25 us from the BS.T_(CO)=T_(mcot,p))—T_(g) and each variable may be defined as follows.

-   -   t₀: a time instant at which the BS starts a transmission.    -   T_(mcot,p): determined by the BS according to section 3.2.    -   T_(g): the total period of all gap periods exceeding 25 us        occurring between a DL transmission of the BS starting from to        and a UL transmission scheduled by the BS and between two UL        transmissions scheduled by the BS.

If the UL transmissions are scheduled in succession, the BS schedulesthe UL transmissions between consecutive subframes in to and t₀+T_(CO).

For the UL transmission on the carrier following the transmission of theBS on the carrier within the duration T_(short_ul)=25 us, the UE mayperform the type 2 CAP for the UL transmission.

If the BS indicates the type 2 CAP for the UE by DCI, the BS indicates achannel access priority class used to obtain access to the channel inthe DCI.

3.3.1.1. Type 1 UL Channel Access Procedure

After sensing that the channel is idle for a slot duration of a deferduration T_(d) and the counter N becomes 0 in step 4, the UE may performa transmission using the type 1 CAP. The counter N is adjusted bysensing the channel for additional slot duration(s) according to thefollowing procedure.

1) Set N=N_(init) where N_(init) is a random number uniformlydistributed between 0 and CW_(p), and go to step 4.

2) If N>0 and the BS chooses to decrement the counter, set N=N−1.

3) Sense the channel for an additional slot duration, and if theadditional slot duration is idle, go to step 4. Else, go to step 5.

4) If N=0, stop. Else, go to step 2.

5) Sense the channel during all slot durations of an additional deferduration T_(d).

6) If the channel is sensed as idle during the slot durations of theadditional defer duration T_(d), go to step 4. Else, go to step 5.

The above-described type 1 UL CAP of the UE may be summarized asfollows.

For a UL transmission, a transmission node (e.g., a UE) may initiate theCAP to operate in LAA SCell(s) which is a U-band cell (S1610).

The UE may randomly select a backoff counter N within a CW according tostep 1. N is set to an initial value N_(init) (S1620). N_(init) is avalue selected randomly from among the values between 0 and CW_(p).

Subsequently, if the backoff counter value N is 0 according to step 4 (Yin S1630), the UE ends the CAP (S1632). Subsequently, the UE may performa Tx burst transmission (S1634). On the other hand, if the backoffcounter value is not 0 (N in S1630), the UE decrements the backoffcounter value by 1 according to step 2 (S1640).

Subsequently, the UE checks whether the channel of the LAA SCell(s) isidle (S1650). If the channel is idle (Y in S1650), the UE checks whetherthe backoff counter value is 0 (S1630).

On the contrary, if the channel is not idle in step S1650, that is, thechannel is busy (N in S1650), the UE checks whether the channel is idlefor a defer duration T_(d) (25 usec or more) longer than a slot time(e.g., 9 usec) according to step 5 (S1660). If the channel is idle forthe defer duration (Y in S1670), the UE may resume the CAP.

For example, if the backoff counter value N_(init) is 10 and the channelis determined to be busy after the backoff counter value is decrementedto 5, the UE determines whether the channel is idle by sensing thechannel for the defer duration. In this case, if the channel is idle forthe defer duration, the UE may perform the CAP again from the backoffcounter value 5 (or from the backoff counter value 4 after decrementingthe backoff counter value by 1), instead of setting the backoff countervalue N_(init).

On the other hand, if the channel is busy for the defer duration (N inS1670), the UE re-performs S1660 to check again whether the channel isidle for a new defer duration.

In the above procedure, if the UE does not perform the transmissionincluding the PUSCH on the carrier in which LAA SCell transmission(s) isperformed after step 4 of the afore-described procedure, the UE mayperform the transmission including the PUSCH on the carrier, when thefollowing conditions are satisfied:

-   -   When the UE is prepared to transmit the transmission including        the PUSCH and the channel is sensed as idle during at least the        slot duration T_(sl); and    -   When the channel is sensed as idle during all slot durations of        the defer duration T_(d) immediately before the transmission        including the PUSCH.

On the contrary, when the UE senses the channel for the first time afterbeing prepared for the transmission, if the channel is not sensed asidle during the slot duration T_(sl), or during any of all slotdurations of the defer duration T_(d) immediately before the intendedtransmission including the PUSCH, the UE proceeds to step 1 aftersensing the channel as idle during the slot durations of the deferduration T_(d).

The defer duration T_(d) includes a duration of T_(f) (=16 us)immediately followed by m_(p) consecutive slot durations where each slotduration T_(sl) is 9 us, and T_(f) includes an idle slot duration T_(sl)at the start of T_(f).

If the UE senses the channel during the slot duration T_(sl) and powermeasured by the UE for at least 4 us in the slot duration is less thanan energy detection threshold X_(Thresh), the slot duration T_(sl) isconsidered to be idle. Otherwise, the slot duration T_(sl) is consideredto be busy.

CW_(min,p)≤CW_(p)≤CW_(max,p) represents a contention window, and CW_(p)adjustment is described in detail in section 3.3.2.

CW_(min,p) and CW_(max,p) are chosen before step 1 of the aboveprocedure.

m_(p), CW_(min,p), and CW_(max,p) are determined based on a channelaccess priority class signaled to the UE (see Table 9).

X_(Thresh) is adjusted according to section 3.3.3.

3.3.1.2. Type 2 UL Channel Access Procedure

If the UE uses the type 2 CAP for a transmission including a PUSCH, theUE may perform the transmission including the PUSCH immediately aftersensing a channel as idle for at least a sensing durationT_(short_ul)=25 us. T_(short_ul) includes a duration of T_(f)(=16 us)immediately followed by one slot duration T_(sl) (=9 us). T_(f) includesan idle slot duration T_(sl) at the start of T_(f). If the channel issensed as idle during the slot duration T_(short_ul), the channel isconsidered to be idle for T_(short_ul).

3.3.2. Contention Window Adjustment Procedure

If the UE performs a transmission using the type 1 CAP associated with achannel access priority class p on a carrier, the UE maintains andadjusts a contention window value CW_(p) using the following proceduresbefore step 1 of the procedure described in section 2.3.1.1. for thetransmission (i.e., before performing the CAP):

-   -   When a new data indicator (NDI) for at least one HARQ process        related to HARQ_ID ref is toggled,    -   Set CW_(p), =CW_(min,p) for all priority classes p∈{1,2,3,4}.    -   Else, increment CW_(p) to the next higher allowed value for all        priority classes p∈{1,2,3,4}.

HARQ_ID ref is the HARQ process ID of a UL-SCH in reference subframen_(ref). Reference subframe n_(ref) is determined as follows.

-   -   When the UE receives a UL grant in subframe n_(g). Here,        subframe n_(w) is the most recent subframe before subframe        n_(g)−3 in which the UE transmits the UL-SCH using the type 1        CAP.    -   If the UE performs a transmission including a UL-SCH without        gaps, starting from subframe no in a subframe n₀, n₁, . . . ,        n_(w), reference subframe n_(ref) is subframe no.

Else, reference subframe n_(ref) is subframe n_(w).

If the UE is scheduled to perform a transmission including a PUSCHwithout gaps in a subframe set n₀, n₁, . . . n_(w−1) and may not performany transmission including the PUSCH in the subframe set, the UE maymaintain CW_(p) for all priority classes p∈{1,2,3,4} without changingCW_(p).

If a reference subframe for the recent scheduled transmission is alsosubframe n_(ref), the UE may maintain CW_(p) for all priority classesp∈{1,2,3,4} equal to CW_(p) for a transmission including a PUSCH, whichuses the recent scheduled type 1 CAP.

If CW_(p)=CW_(max,p) the next higher allowed value for the CW_(p)adjustment is CW_(max,p).

If CW_(p)=CW_(max,p) is used K times consecutively to generate N_(init),only CW_(p) for a priority class p for CW_(p)=CW_(max,p) used K timesconsecutively to generate N_(init) is reset to CW_(min,p). K is thenselected by the UE from a set of {1, 2, . . . , 8} values for eachpriority class p∈{1,2,3,4}.

3.3.3. Energy Detection Threshold Adaptation procedure)

A UE accessing a carrier on which a LAA SCell transmission is performedsets an energy detection threshold X_(Thresh) to a maximum energydetection threshold X_(Thresh_max) or less.

The maximum energy detection threshold X_(Thresh_max) is determined asfollows.

-   -   If the UE is configured with a higher-layer parameter        ‘maxEnergyDetectionThreshold-r14’,    -   X_(Thresh_max) is set equal to a value signaled by the        higher-layer parameter.    -   Else,        -   The UE determines X′_(Thresh_max) according to the procedure            described in section 3.3.3.1.        -   If the UE is configured with a higher-layer parameter            maxEnergyDetectionThresholdOffset-r14′,        -   X_(Thresh_max) is set to X′_(Thresh_max) adjusted according            to an offset value signaled by the higher-layer parameter.        -   Else,        -   The UE sets X_(Thresh_max)=X′_(Thresh_max).

3.3.3.1. Default Maximum Energy Detection Threshold ComputationProcedure

If a higher-layer parameter ‘ab senceOfAnyOtherTechnology-r14’ indicatesTRUE:

$X_{T{hresh\_ ma}x}^{\prime} = {\min\begin{Bmatrix}{{T_{\max} + {10{dB}}},} \\X_{r}\end{Bmatrix}}$

where Xr is a maximum energy detection threshold (in dBm) defined inregulatory requirements when the regulation is defined. ElseX_(r)=T_(max)+10 dB.

Else:

$X_{T{hres\_ ma}x}^{\prime} = {\max\begin{Bmatrix}{{{- 72} + {{10 \cdot \log}10\left( {{{BW}{MHz}}/20{MHz}} \right){dBm}}},} \\{\min\begin{Bmatrix}{T_{\max},} \\{T_{\max} - T_{a} + \left( {P_{H} + {{10 \cdot \log}10\left( {{{BW}{MHz}}/20{MHz}} \right)} - P_{TX}} \right.}\end{Bmatrix}}\end{Bmatrix}}$

Here, each variable is defined as follows.

-   -   T_(A)=10 dB    -   P_(H)=23 dBm;    -   P_(TX) is the set to the value of P_(CMAX__H,c) as define in        3GPP TS 36.101.        T _(max) (dBm)=10·log 10(3.16228·10⁻⁸(mW/MHz)·BWMHz(MHz))        -   BWMHz is the single carrier bandwidth in MHz.

3.4. Subframe/Slot Structure Applicable to Unlicensed Band System

FIG. 17 is a diagram illustrating a partial TTI or a partialsubframe/slot applicable to the present disclosure.

In the Release-13 LAA system, a partial TTI is defined as a DwPTS tomaximize use of MCOT and support continuous transmission in a DL bursttransmission. The partial TTI (or partial subframe) refers to a periodin which a PDSCH signal is transmitted for a length smaller than alegacy TTI (e.g., 1 ms).

In the present disclosure, a starting partial TTI or a starting partialsubframe/slot refers to a form in which some front symbols of a subframeare emptied, and an ending partial TTI or ending partial subframe/slotrefers to a form in which some symbols at the end of a subframe areemptied. (On the other hand, a whole TTI is called a normal TTI or afull TTI.)

FIG. 17 illustrates various forms of the above-described partial TTI.The first drawing of FIG. 17 illustrates the ending partial TTI (orsubframe/slot), and the second drawing of FIG. 17 illustrates thestarting partial TTI (or subframe/slot). In addition, the third drawingof FIG. 17 illustrates a partial TTI (or subframe/slot) configured byemptying some symbols at the start and end of the subframe/slot. In thiscase, a time interval excluding signal transmission in a normal TTI iscalled a transmission gap (Tx gap).

While FIG. 17 has been described in the context of a DL operation, thesame thing may be applied to a UL operation. For example, the partialTTI structures illustrated in FIG. 16 may also be applied to PUCCHand/or PUSCH transmission.

4. PROPOSED EMBODIMENTS

Hereinafter, the configurations according to the present disclosure willbe described in detail based on the above-described technical features.

Cellular communication system such as the LTE/NR system to which thepresent disclosure is applicable support use of a U-band of 2.4 GHz,which is commonly used in the conventional Wi-Fi system, or a U-band of5 or 60 GHz in traffic offloading.

Due to the characteristics of a U-band, each communication node needs toperform channel sensing before transmitting a signal to check whetherother communication nodes perform signal transmission in thecorresponding U-band. Such operation may be referred to as listen beforetalk (LBT) or a channel access procedure (CAP). That is, a BS or a UEneeds to perform the LBT or CAP to transmit a signal in a U-band. Inaddition, when the BS or UE performs signal transmission as describedabove, other communication nodes such as a Wi-Fi node, etc. also need toperform the LBT or CAP to avoid causing interference to the BS or UE.

In the NR system to which the present disclosure is applicable, a BS ora UE may transmit and receive beamformed signals using multiple antennas(in particular, in a mmWave band). In this case, a transmitting side mayperform beam sweeping on analog beams capable of covering some of thewhole cell coverage over multiple TUs so that the transmitting side maytransmit a signal capable of covering the whole cell coverage.

In the present disclosure, a wireless communication system supporting aU-band may mean both that the wireless communication system supports oneor more U-bands only or that the wireless communication system supportsone L-band and one or more U-bands. Thus, a U-band according to thepresent disclosure may act as a PCell or an SCell in a wirelesscommunication system to which the present disclosure is applicable.

Herein, a signal continuously transmitted in the time domain with no gapin a U-band is referred to as a transmission (Tx) burst. The presentdisclosure describes a method of transmitting and receiving an initialsignal for informing transmission of a Tx burst between a transmittingside and a receiving side (particularly, when the transmitting andreceiving sides are a BS and a UE, respectively) and a method ofmonitoring a PDCCH based on the initial signal.

4.1. Initial Signal Transmission and Reception Method

4.1.1. Purpose of Initial Signal Transmission

In an L-band (or licensed carrier), periodicity may be guaranteed atleast for a signal/channel that needs to be periodically transmittedsuch as a reference signal for measurement. However, in a U-band (orunlicensed carrier), if a transmitting side fails in a CAP (or LBT), thetransmitting side may not attempt signal transmission. Thus, a signalfor informing whether there is a signal to be transmitted in the U-bandmay be required. In particular, since the NR system has no steadilytransmitted signals such as a cell-specific reference signal (CRS)compared to the LTE system, the following signals proposed in thepresent disclosure may be necessary.

In the present disclosure, a signal for informing that a transmittingside will perform signal transmission (or is performing signaltransmission) in a U-band is referred to as an initial signal. In someembodiments, such a signal may be referred to as a notification signal,etc.

The initial signal may be transmitted in the front part of a Tx burst orin each specific TU (e.g., at each slot boundary) of the Tx burst.

Such an initial signal may be transmitted not only for the purpose ofinforming that a transmitting side transmits a signal in a U-band basedon a CAP but also for the following purposes.

-   -   Tx beam identification: A receiving side may recognize whether a        transmitting side transmits a Tx burst and which Tx beam the        transmitting side uses, based on an initial signal transmitted        from the transmitting side.    -   Automatic gain control (AGC) gain setting: A receiving side may        perform AGC gain setting for receiving a Tx burst, which is        transmitted after transmission of an initial signal, based on        the initial signal.    -   (Coarse or fine) Time and/or frequency synchronization: An        initial signal may be used to obtain accurate time/frequency        synchronization or frame/subframe/slot/symbol boundaries for a        periodically transmitted signal (e.g., a signal for radio        resource management (RRM) measurement, a signal for channel        state information (CSI) measurement, etc.). Alternatively, a        specific node may attempt to detect an initial signal without        performing a fast Fourier transform (FFT) for received signals        but perform the FFT only when the initial signal is detected. By        doing so, the specific node may have an advantage in power        saving.    -   Notification of neighbor cells/other operators/other RATs:        According to the present disclosure, a receiving side belonging        to a neighbor cell/another operator/another RAT may detect an        initial signal of a wireless communication system such as the NR        system by performing an FFT without consideration of the        numerology supported in the wireless communication system.        Specifically, when a DL initial signal is configured as in the        following fifth DL initial signal transmission and reception        method, a receiving side may detect the initial signal by        correlating received signals in the time domain (for example,        when an initial signal is repeated every X usec, the receiving        side may receive a signal with a length of X usec, store the        signal in a buffer, correlate the signal with a next signal with        the same length, and recognize/know from the repeatedly        transmitted initial signal whether there is a DL Tx burst). This        may be advantageous in coexistence with neighbor cells/other        operators/other RATs.

4.1.2. Initial Signal Transmission and Reception Method for DL SignalTransmission

In this section, a description will be given of signal transmission andreception methods using, as an initial signal for DL signaltransmission, a system synchronization signal or a signal modified basedthereon, a demodulation reference signal (DM-RS) related to a broadcastchannel or a signal/channel modified based thereon, a DM-RS related to aPDCCH or a signal/channel modified based thereon, a channel stateinformation reference signal (CSI-RS) or a signal modified basedthereon, a signal in a DL Tx burst or a signal modified based thereon,etc. In this case, such an initial signal may be transmitted from a BSthat performs (or succeeds in) the DL CAP proposed in the presentdisclosure.

4.1.2.1. First DL Initial Signal Transmission and Reception Method:Modification of PSS and/or SSS for Use of Initial Signal

In the NR system to which the present disclosure is applicable, aPSS/SSS includes 12 RBs (and more particularly, the PSS/SSS isconfigured with a 127-length sequence) and has the same sequence foreach beam. Considering regulations related to the power spectral density(PSD) in U-bands, more power may be assigned by spreading andtransmitting a signal in the frequency domain. Thus, an initial signalmay be defined by performing RB (RE, RE-group, or RB-group) interlacingon the PSS/SSS, repeating the PSS/SSS in the frequency domain, orincreasing the length of the PSS/SSS sequence. Here, the RB (RE,RE-group, or RB-group) interlacing may refer to an operation ofconfiguring one cluster on an RB (RE, RE-group, or RB-group) basis andspreading a signal in the frequency domain by applying a predeterminedfrequency-domain interval to each cluster.

In particular, when a Tx beam applied to a Tx burst is capable of beingidentified based on the initial signal, the initial signal may bedefined based on a difference sequence for each beam.

For example, the initial signal applicable to the present disclosure maybe defined by changing a PSS/SSS sequence formula defined in the LTE orNR system to a function of beam indices (e.g., “cell index+beam index”is used instead of the cell index).

As another example, the initial signal applicable to the presentdisclosure may be defined by determining the starting PRB (or RE) indexof the PSS/SSS defined in the LTE or NR system as a function of beamindices (e.g., starting PRB index=X+beam index, where X may bepredefined or signaled by higher layer signaling (e.g., RRC, DCI,etc.)).

As a further example, the initial signal applicable to the presentdisclosure may be defined by determining the starting PRB (or RE) indexof the PSS/SSS defined in the LTE or NR system as a function of beamindices and/or cell indices (e.g., starting PRB index=X+beam index+mod(cell index, 4), where X may be predefined or signaled by higher layersignaling (e.g., RRC, DCI, etc.)) in consideration of interferencebetween serving and neighbor cells.

For distinction between the initial signal and the PSS/SSS forsynchronization in the serving cell, the initial signal may betransmitted in a frequency region different from that for the PSS/SSS(that is, the initial signal may not be transmitted in a synchronizationraster).

Additionally, the initial signal applicable to the present disclosuremay be defined by multiplexing of the PSS and SSS in the time and/orfrequency domain after applying the above-described method to the PSSand SSS.

4.1.2.2. Second DL Initial Signal Transmission and Reception Method:Modification of PBCH DM-RS for Use of Initial Signal

In the NR system to which the present disclosure is applicable, a PBCHDM-RS may include up to 20 RBs and have a different sequence for eachbeam (a total of 8 sequences are defined).

As described above, considering the regulations related to the powerspectral density (PSD) in U-bands, more power may be assigned byspreading and transmitting a signal in the frequency domain. Thus, aninitial signal may be defined by performing RB (RE or RB-group)interlacing on the PBCH DM-RS composed of 20 RBs, repeating the PBCHDM-RS in the frequency domain, or increasing the length of the PBCHDM-RS sequence.

In particular, when a Tx beam applied to a Tx burst is capable of beingidentified based on the initial signal, the initial signal may bedefined based on a difference sequence for each beam. When atransmitting side transmits the initial signal using 9 or more beams,the initial signal transmitted on each beam may be defined as follows.

For example, the initial signal applicable to the present disclosure maybe defined by determining the starting PRB (or RE) index of the PBCHDM-RS defined in the LTE or NR system as a function of beam indices(e.g., starting PRB index=X+beam index/8, where X may be predefined orsignaled by higher layer signaling (e.g., RRC, DCI, etc.)).

As another example, the initial signal applicable to the presentdisclosure may be defined by determining the starting PRB (or RE) indexof the PBCH DM-RS defined in the LTE or NR system as a function of beamindices and/or cell indices (e.g., starting PRB index=X+beam index/8+mod(cell index, 4), where X may be predefined or signaled by higher layersignaling (e.g., RRC, DCI, etc.)) in consideration of interferencebetween serving and neighbor cells.

For distinction between the initial signal and the PBCH DM-RS forsynchronization in the serving cell, the initial signal may betransmitted in a frequency region different from that for the PBCH DM-RS(that is, the initial signal may not be transmitted in a synchronizationraster).

Additionally, the initial signal applicable to the present disclosuremay be defined by multiplexing of a plurality of PBCH DM-RSs in the timeand/or frequency domain after applying the above-described method to thePBCH DM-RSs.

4.1.2.3. Third DL Initial Signal Transmission and Reception Method:Modification of PDCCH DM-RS for Use of Initial Signal

In the NR system to which the present disclosure is applicable, when theprecoder granularity of a PDCCH is set as consecutive RBs in thefrequency domain in a CORESET configuration (regardless of resourceelement group (REG) bundle sizes), if transmission is performed in oneREG among the consecutive RBs, a PDCCH DM-RS may be transmitted in allof the consecutive RBs.

In the present disclosure, the PDCCH DM-RS may be used as an initialsignal.

Alternatively, the PDCCH DM-RS and the PDCCH corresponding thereto maybe used as the initial signal (or a channel used as the initial signal).

Specifically, a UE may decode the PDCCH by detecting the PDCCH DM-RSdefined as the initial signal in a specific CORESET configuration (or asearch space set configuration associated with the correspondingCORESET). In this case, if a cyclic redundancy check (CRC) issuccessful, the UE may recognize that a DL Tx burst is transmitted in acorresponding slot.

In this configuration, a group common PDCCH including slot formatindicator (SFI) information may be used as the PDCCH. The SFIinformation may include information on a channel occupancy time (COT)occupied by a BS, information on the configurations ofDL/UL/flexible/reserved symbols in the COT, etc.

The CORESET may be configured in at least M RBs (e.g., M=50) or afrequency band of W MHz or higher (e.g., W=10) in consideration of thetransmission power of the initial signal.

In this case, the CORESET may include only one (OFDM) symbol to minimizeoccupancy in the time domain. In the following description, a symbol maybe referred to as an OFDM symbol.

Additionally, for AGC gain setting for Tx burst reception, a DM-RS maybe transmitted without (or with) a PDCCH in K symbols (e.g., K=1) beforethe PDCCH is transmitted (or before L symbols from the time when thePDCCH is transmitted). In this case, the DM-RS transmitted together withthe PDCCH (e.g., the DM-RS transmitted when the PDCCH is transmitted)may not be defined as the initial signal.

Additionally, the initial signal applicable to the present disclosuremay be defined by multiplexing of multiple PDCCH DM-RSs in the timeand/or frequency domain after applying the above-described method to thePDCCH DM-RSs.

In the present disclosure, a CORESET configuration may include atime/frequency resource region in which a PDCCH may be transmitted,information on whether interleaving is applied, precoder granularity, anREG bundle size, a QCL relationship between SSBs or RSs, etc. A searchspace configuration may include a CORESET index, the number of PDCCHblind decoding (BD) candidates per aggregation level, information on aPDCCH monitoring periodicity/offset/occasion, etc.

4.1.2.4. Fourth DL Initial Signal Transmission and Reception Method: Useof Cell-Specific CSI-RS as Initial Signal

In the NR system to which the present disclosure is applicable, a CSI-RSmay be transmitted and received based on sequence information configuredin a resource region, which is configured by a UE-specific RRCconfiguration. In this case, a cell-specific CSI-RS may be definedseparately under consideration of an idle-state UE that needs to receivean initial signal with no separate RRC configuration. Alternatively, thecell-specific CSI-RS may be defined separately by the resource andsequence information of the CSI-RS, which is determined based on afunction of cell IDs and beam IDs.

The cell-specific CSI-RS may be used as the initial signal.

4.1.2.5. Fifth DL Initial Signal Transmission and Reception Method:Repeated Transmission of CP of Symbol in DL Tx Burst or Part Thereof asInitial Signal

A BS may transmit, as an initial signal, a CP of the first symbol in aDL Tx burst or a part of the corresponding CP. Upon receiving theinitial signal, a UE may obtain time synchronization based on therepeated pattern of the initial signal. Then, the UE may achieve finetime/frequency synchronization for channels/signals in the following DLTx burst.

Specifically, when the subcarrier spacing is 15 kHz, the CP length maybe set to 144 T_s or 160 T_s (where T_(s)=1/2048/15 k sec). The BS maytransmit the DL Tx burst after transmitting a signal shorter than orequal to 144 T_s (or 160 T_s) N times. In this case, the value of N (orthe minimum and/or maximum value of N) may be predefined or configuredby RRC signaling.

Alternatively, when a signal shorter than 144 T_s (or 160 T_s) is used(for example, P T_s, where P<144 or 160), the most preceding signal intime among CP signals with the length of 144 T_s (or 160 T_s) may bedefined as the initial signal. In this case, the value of P (or theminimum and/or maximum value of P) may be predefined or configured byRRC signaling.

In this case, since the CP transmitted immediately after the initialsignal is repeatedly transmitted N times may be equivalent to (orinclude) the initial signal although the number of times that theinitial signal is actually repeated is N, the same effect as if theinitial signal is repeated N+1 times may be obtained.

Further, the BS may map specific additional information (e.g., signatureinformation, etc.) to the initial signal and then transmit the initialsignal to the UE. To this end, the BS may multiply a specific orthogonalcover code to the initial signal in the time domain and then transmitthe initial signal to the UE. For example, when the BS applies alength-N cover code to the initial signal (or repeatedly applies alength-N/K cover code K times), information corresponding to each covercode applied to the initial signal may be used to identify an operator,a beam ID, an indicator indicating a UE (group) that needs to receivethe following DL Tx burst, etc.

The initial signal according to the above-described embodiments may betransmitted before the DL Tx burst including DL signals/channels to bereceived by idle-mode UEs (and/or an inactive-state UEs). In otherwords, the BS may transmit the initial signal before the DL Tx burstincluding the DL signals/channels.

For example, the BS may transmit the initial signal before transmittingthe DL Tx burst including PDCCHs/PDSCHs associated with paginginformation that the idle-mode UEs (and/or an inactive-state UEs) needto read after wake-up. In this case, since the signal transmission isperformed in a U-band, the BS may perform a DL CAP for the DL Tx bursttransmission and transmit the DL Tx burst when the DL CAP is successful.

Thus, when UEs are configured/instructed to read the paging information,the UEs may expect to receive the DL Tx burst including thePDCCHs/PDSCHs associated with the paging information upon receiving theinitial signal. While receiving the initial signal, the UEs may obtaintime synchronization.

Alternatively, the idle-mode UEs (and/or an inactive-state UEs) mayrequire a predetermined time (e.g., a processing (or warm-up) time) fornext signal reception after receiving the initial signal. Thus, theinitial signal may be transmitted the predetermined time before thestart of the DL Tx burst including the DL signals/channels to bereceived by the idle-mode UEs (and/or an inactive-state UEs) rather thanimmediately before the start of the DL Tx burst. In this case, thepredetermined time may be predefined or configured by RRC signaling.

4.1.3. Initial Signal Transmission and Reception Method for UL SignalTransmission

In this section, initial signal transmission and reception methods willbe described in detail from the perspective of UL signal transmission.When a UE attempts UL signal transmission according to UL grant-basedscheduling from a BS, the UE may be assigned UE Tx beams from the BS.

However, since it may be difficult for the BS to anticipate UL CAPresults of the UE, the following operation may be allowed. That is, theBS may indicate a predetermined number of UE Tx beam candidates to theUE through a UL grant (L1 signaling such as a group common PDCCH, higherlayer signaling such as RRC signaling, etc.), and the UE may performtransmission by selecting a Tx beam based on the UL CAP results.

Hereinafter, a description will be given of UL initial signaltransmission and reception methods applicable when UL transmission isperformed in U-bands.

4.1.3.1. First UL Initial Signal Transmission and Reception Method:Distinction Between UE Tx Beams Based on UL DM-RS (or Sounding ReferenceSignal (SRS)) Sequences

When a BS informs a UE of UE Tx beam candidates through a UL grant (L1signaling such as a group common PDCCH, higher layer signaling such asRRC signaling, etc.) (for example, when the BS signals Tx beam #0 and Txbeam #1 to the UE), the UE may transmit an initial signal based on a ULDM-RS (or SRS) sequence corresponding to the index of a Tx beam used forUL transmission after succeeding in a UL CAP. In this case, the UL DM-RS(or SRS) sequence may be generated by a function of Tx beam indices(e.g., Tx cyclic shift index=indicated index+Tx beam index).

4.1.3.2. Second UL Initial Signal Transmission and Reception Method:Distinction Between UE Tx Beams Based on Frequency Indices of UL DM-RS(or SRS) Sequences

When a BS informs a UE of UE Tx beam candidates through a UL grant (L1signaling such as a group common PDCCH, higher layer signaling such asRRC signaling, etc.) (for example, when the BS signals Tx beam #0 and Txbeam #1 to the UE), the UE may transmit an initial signal based on a ULDM-RS (or SRS) sequence on a frequency index (or port number)corresponding to the index of a Tx beam used for UL transmission aftersucceeding in a UL CAP.

For example, when the UE uses Tx beam #0 for the UL transmission aftersucceeding in the UL CAP, the UE may transmit the initial signal (e.g.,UL DM-RS, SRS, etc.) in REs with even indices. When the UE uses Tx beam#1 for the UL transmission after succeeding in the UL CAP, the UE maytransmit the initial signal (e.g., UL DM-RS, SRS, etc.) in REs with oddindices.

Alternatively, although the UE may transmit the initial signal onfrequency resources (e.g., even-indexed REs) corresponding to Tx beam #0and all frequency resources (e.g., odd-indexed REs) corresponding to Txbeam #1 after succeeding in the UL CAP regardless of whether the Tx beamused for the UL transmission is Tx beam #0 or Tx beam #1, the UE mayinform the BS of the index of a Tx beam actually used for thetransmission by changing the sequence of the initial signal.

4.1.3.3. Third UL Initial Signal Transmission and Reception Method:Distinction Between UE Tx Beams Based on Time Resources for TransmittingUL DM-RS (or SRS) Sequences

When a BS informs a UE of UE Tx beam candidates through a UL grant (L1signaling such as a group common PDCCH, higher layer signaling such asRRC signaling, etc.) (for example, when the BS signals Tx beam #0 and Txbeam #1 to the UE), the UE may transmit an initial signal based on a ULDM-RS (or SRS) sequence on a time resource (e.g., symbol index)corresponding to the index of a Tx beam used for UL transmission aftersucceeding in a UL CAP.

For example, when the UE uses Tx beam #0 for the UL transmission aftersucceeding in the UL CAP, the UE may transmit the initial signal (e.g.,UL DM-RS, SRS, etc.) in symbol #0 in a corresponding slot. When the UEuses Tx beam #1 for the UL transmission after succeeding in the UL CAP,the UE may transmit the initial signal (e.g., UL DM-RS, SRS, etc.) insymbol #1 in the corresponding slot.

Alternatively, although the UE may transmit the initial signal on timeresources (e.g., symbol #0 in the slot) corresponding to Tx beam #0 andall (or some available) resources (e.g., symbol #1 in the slot)corresponding to Tx beam #1 after succeeding in the UL CAP regardless ofwhether the Tx beam used for the UL transmission is Tx beam #0 or Txbeam #1, the UE may inform the BS of the index of a Tx beam actuallyused for the transmission by changing the sequence of the initialsignal.

In the above-described UL initial signal transmission and receptionmethods, the BS may indicate the indices of UE Tx beams associated withSRS resources through an SRS resource indicator (SRI) in the UL grant inorder to inform the UE of UE Tx beam candidates

Additionally, the initial signal applicable to the present disclosuremay be defined by multiplexing of multiple UL DM-RSs (or SRSs) in thetime and/or frequency domain after applying the above-described methodto the UL DM-RSs (or SRSs).

4.2. PDCCH Monitoring Method

In this section, a description will be given of how a BS indicates a Txbeam and how a UE receives a PDCCH when an initial signal is definedbased on a PDCCH DM-RS according to the DL initial signal transmissionand reception method described in section 4.1.2.3. Further, a method bywhich a UE monitors a PDCCH in a DL Tx burst will be also described indetail.

When a BS and a UE transmit and receive a signal by forming an analogbeam (and more particularly, in a mmWave band), if only one beam pairlink is established between the BS and UE or if the link quality of thebeam pair is degraded due to the following reasons: mobility, blockage,etc., it may be difficult to find a new beam pair link between the BSand UE. Accordingly, multiple beam pair links may be established betweenthe BS and UE. In this case, even though the link equality of a beampair link is degraded, another beam pair link with better quality may begenerated.

It is assumed that up to N CORESETs (e.g., N=3) may be configured foreach BWP in the NR system to which the present disclosure is applicable.In this case, the BS may configure QCL SSBs or RSs (e.g., CSI-RS) forthe UE. In particular, as described above, when the BS and UE intends toestablish multiple beam pair links therebetween, the BS may configure adifferent QCL relationship for each CORESET. In this case, which Tx beamis used by the BS to transmit a DL Tx burst (or which SSB or RS is QCL(or QCLed) with a CORESET for transmission thereof) may vary dependingon CAP results. As a result, the UE may not understand which CORESET istransmitted at which time.

Alternatively, the BS may configure a search space set corresponding toa CORESET index. However, the UE may not anticipate which search spaceset is transmitted.

In this section, a described will be given of how a BS indicates a Txbeam and how a UE receives a PDCCH when DL initial signal transmissionand reception are defined based on a PDCCH DM-RS as described in section4.1.2.3,

4.2.1. DL Tx Beam Indication Method

4.2.1.1. First DL Tx Beam Indication Method

It is assumed that CORESETs (or search space sets) corresponding to aplurality of Tx beams (or having different QCL relationships) in oneslot (a TU or a symbol group) are time division multiplexed (TDMed)(and/or frequency division multiplexed (FDMed)). When an initial signaland/or a PDCCH is detected in a CORESET (or search space set) in aU-band, a UE may receive a DL data burst on an Rx beam corresponding tothe CORESET (or by assuming that the UE receives a signal transmitted ona Tx beam QCL (or QCLed) with the corresponding CORESET). In this case,a BS may indicate only a CORESET (or search space set) corresponding toa Tx beam to be actually used for DL data burst transmission based onthe success of a DL CAP among the TDMed (and/or FDMed) CORESETs (havingthe different QCL relationship). In other words, the UE may not performPDCCH monitoring for CORESETs associated with other Tx beams except theTx beam associated with the CORESET detected during the corresponding DLdata burst transmission (in this case, information on the DLtransmission duration of the corresponding DL data burst may be obtainedfrom the initial signal or a specific PDCCH such as a group commonPDCCH).

The operation in which the BS transmits a DL signal only on a Tx beamassociated with a CORESET in a specific DL data burst or the operationin which the UE receives the DL signal based on the Tx beam associatedwith the CORESET in the specific DL data burst in response to the BSoperation may be applied not only to the method proposed in section4.2.1.1 but also the methods proposed in section 4.2.1.2 or 4.2.1.3.

4.2.1.2. Second DL Tx Beam Indication Method

It is assumed that one default beam (or CORESET(s) with one default QCLrelationship) is configured/defined for a UE. In this case, the UE mayreceive a PDCCH on the default beam (or a beam applied to the CORESET(s)with the default QCL relationship) on most PDCCH monitoring occasions(or at slot boundaries). However, in a specific PDCCH monitoringoccasion (or at a specific symbol boundary in a slot), the UE mayreceive the PDCCH on another configured beam (or receive a CORESET withanother QCL relationship).

Alternatively, the UE may receive a CORESET based on a predeterminedslot-to-CORESET relationship. For example, when there are three CORESETsassociated with three beams (or having different QCL relationships), theUE may configure an Rx beam (or receive the CORESET) based on the indexof the start slot of a DL burst according to the following relationship:CORESET index=mod (slot index, 3). Here, a CORESET may be replaced witha search space set associated with the CORESET.

4.2.1.3. Third DL Tx Beam Indication Method

It is assumed that CORESETs (or search space sets) corresponding to aplurality of Tx beams (or having different QCL relationships) in oneslot (a TU or a symbol group) are TDMed (and/or FDMed). When an initialsignal and/or a PDCCH is detected in a CORESET (or search space set) ina U-band, if the initial signal and/or PDCCH in the correspondingCORESET contains information indicating that a Tx beam applied to theCORESET is identical to a Tx beam applied to a data burst, a UE mayreceive the DL data burst on an Rx beam corresponding to the CORESET (oron the assumption that a signal transmitted on a Tx beam QCL (or QCLed)with the corresponding CORESET is received). In other words, when theinitial signal and/or PDCCH in the corresponding CORESET does notcontain the information indicating that the Tx beam applied to theCORESET is identical to the Tx beam applied to the data burst, the UEmay not attempt to receive the data burst on the beam associated withthe corresponding CORESET although the initial signal and/or PDCCH isincluded in the CORESET detected by the UE.

A BS may transmit the initial signal and/or PDCCH not only for a CORESETcorresponding to a Tx beam to be actually used for DL data bursttransmission based on the success of a DL CAP among the TDMed (and/orFDMed) CORESETs (having the different QCL relationship) but also for all(or some) TDMed CORESETs. In this case, depending on whether the Tx beamapplied to the initial signal and/or PDCCH is identical to the Tx beamapplied to the DL data burst, the BS may include different informationin the sequence of the initial signal and/or the PDCCH. If the UErecognizes, from the information included in the sequence of the initialsignal and/or the PDCCH, that the Tx beam applied to the initial signaland/or PDCCH is different from the Tx beam applied to the data burst,the UE may expect that no data burst will be transmitted on thecorresponding Tx beam (or all Tx beams available for a predeterminedtime) for the predetermined time (e.g., during one slot or until theboundary of an end slot). Here, a CORESET may be replaced with a searchspace set associated with the CORESET.

In the above-described beam indication methods, a CORESET may refer to aCORESET (or search space set) in which a group common PDCCH includingSFI information is transmitted. In other words, in the beam indicationmethods, a PDCCH may refer to a group common PDCCH including SFIinformation.

The beam indication methods may be equally applied not only to theinitial signal based on the PDCCH DM-RS described in section 4.1.2.3 butalso to other DL initial signals. For example, when signals obtained bymodifying a PSS/SSS/PBCH-DM-RS are defined as initial signals asdescribed in section 4.1.2.1 or 4.1.2.2 and when the index of aslot/symbol in which the corresponding signals are transmitted throughTDM (or FDM) is predefined, a BS may inform a UE of the index of a beamused for a burst by transmitting some or all of the initial signals.

4.2.2. PDCCH Monitoring Method

Hereinafter, a description will be given of a method by which a UEreceives (or monitors) a PDCCH based on the above-described variousmethods.

4.2.2.1. First PDCCH Monitoring Method

If a UE recognize the start of a DL burst while performing PDCCHmonitoring in a U-band at a default periodicity (or at a PDCCHperiodicity configured in a default search space set), the UE mayperform the PDCCH monitoring on a slot basis (or at a PDCCH periodicityconfigured in a search space set configured to be transmitted in the DLburst) from a next slot (or after k slots) (in the DL burst).

Here, the default periodicity may be shorter than one slot duration andindicated/configured by L1 signaling or RRC signaling.

FIG. 18 is a diagram schematically illustrating a PDCCH monitoringoperation for a UE applicable to the present disclosure.

As illustrated in FIG. 18 , UE 1 may be configured to perform PDCCHmonitoring four times in one slot. Upon recognizing that a data burststarts in slot #n (and slot #n+3), UE 1 may perform the PDCCH monitoringon a slot basis from slot #n+1 (unlike the configuration).

UE 2 may be configured to perform the PDCCH monitoring two times in oneslot. Upon recognizing that the data burst starts in slot #n (and slot#n+3), UE 2 may perform the PDCCH monitoring on the slot basis from slot#n+1 (unlike the configuration).

UE 3 may be configured to perform the PDCCH monitoring four times in oneslot as in UE 1. However, it is assumed that UE 3 fails to recognizethat a BS starts the data burst, as opposed to UE 1 and UE 2. In thiscase, since UE 3 does not recognize that the BS starts the data burst,UE 3 may continue to perform the PDCCH monitoring at a periodicityshorter than one slot.

UE 1 to UE 3 may recognize the start of a data burst based on an initialsignal from the BS in the same way as described above or according toother methods.

According to the present disclosure, since a UE is capable of performingPDCCH decoding only at slot boundaries within a data burst (or COT) uponrecognizing the burst, the UE may have advantages in terms of powersaving and spectral efficiency due to DCI overhead reduction in aslot/mini-slot.

4.2.2.2. Second PDCCH Monitoring Method

A BS may indicate/configure the periodicity of PDCCH monitoring to beperformed in a Tx burst or the configuration of a search space setto/for a UE over a PDCCH (e.g., a group common PDCCH containing SFIinformation).

For example, referring to FIG. 18 , the BS may transmit a PDCCH to oneor more UEs in slot #n in order to indicate/configure the periodicity ofPDCCH monitoring to be performed in slot #n+1 to/for the UEs receivingthe PDCCH.

Alternatively, when the UE receives a PDCCH containing information on asearch space set while performing the PDCCH monitoring at the defaultperiodicity (or the PDCCH periodicity configured in the default searchspace set), the UE may perform the PDCCH monitoring based on a PDCCHperiodicity/offset configured in the corresponding search space set(from a slot in which the corresponding PDCCH is transmitted or after Kslot(s) from the slot in which the corresponding PDCCH is transmitted).

In the above-described first PDCCH monitoring method, a UE may fail todetect/decode a PDCCH and/or an initial signal that indicates the startof a Tx burst. However, to allow such a UE to perform PDCCH detection atslot boundaries at least in a next slot (or in a slot after next kslots), PDCCH candidates of a CORESET for the PDCCH monitoring in eachslot (or at each slot boundary) may have a relationship of inclusionwith PDCCH candidates of a CORESET for the PDCCH monitoring at thedefault periodicity. For example, the PDCCH candidates of the CORESETfor the PDCCH monitoring in each slot (or at each slot boundary) may beconfigured to include PDCCH candidates (at least) at slot boundariesamong the PDCCH candidates of the CORESET for the PDCCH monitoring atthe default periodicity. On the contrary, the PDCCH candidates (atleast) at the slot boundaries among the PDCCH candidates of the CORESETfor the PDCCH monitoring at the default periodicity may be configured toinclude the PDCCH candidates of the CORESET for the PDCCH monitoring ineach slot (or at each slot boundary). Alternatively, the PDCCHcandidates of the CORESET for the PDCCH monitoring in each slot (or ateach slot boundary) and the PDCCH candidates (at least) at the slotboundaries among the PDCCH candidates of the CORESET for the PDCCHmonitoring at the default periodicity may be configured to partiallyoverlap with each other.

Similarly, in the above-described first PDCCH monitoring method, a UEmay fail to detect/decode a PDCCH that indicates/configures a PDCCHmonitoring periodicity or a search space configuration. However, toallow such a UE to perform PDCCH detection at slot boundaries at leastin a next slot (or in next k slots), PDCCH candidates of a CORESET forthe PDCCH monitoring in each slot (or at each slot boundary) may have arelationship of inclusion with PDCCH candidates (at least) at slotboundaries among PDCCH candidates of a CORESET for the PDCCH monitoringat the periodicity shorter than the slot. For example, the PDCCHcandidates of the CORESET for the PDCCH monitoring in each slot (or ateach slot boundary) may be configured to include the PDCCH candidates(at least) at the slot boundaries among the PDCCH candidates of theCORESET for the PDCCH monitoring at the periodicity shorter than theslot. On the contrary, the PDCCH candidates (at least) at the slotboundaries among the PDCCH candidates of the CORESET for the PDCCHmonitoring at the periodicity shorter than the slot may be configured toinclude the PDCCH candidates of the CORESET for the PDCCH monitoring ineach slot (or at each slot boundary). Alternatively, the PDCCHcandidates of the CORESET for the PDCCH monitoring in each slot (or ateach slot boundary) and the PDCCH candidates (at least) at the slotboundaries among the PDCCH candidates of the CORESET for the PDCCHmonitoring at the periodicity shorter than the slot may be configured topartially overlap with each other.

4.3. Embodiment Applicable to Present Disclosure

FIG. 19 is a diagram illustrating a signal transmission and receptionmethod for a UE and a BS in a U-band applicable to the presentdisclosure, FIG. 20 is a flowchart illustrating a method for the UE toreceive a DL signal in the U-band applicable to the present disclosure,and FIG. 21 is a flowchart illustrating a method for the BS to transmitthe DL signal in the U-band applicable to the present disclosure.

According to the present disclosure, the UE may receive the DL signal byperforming first PDCCH monitoring at a first periodicity in the U-band(S1910 and S2010).

In this case, the BS may perform a CAP for transmitting the DL signal inthe U-band (S1915 and S2110). In the present disclosure, step S1910 andS1915 may be performed sequentially or simultaneously.

The BS transmits an initial signal based on the DL CAP (S1920 andS2120).

Specifically, when the BS determines from the DL CAP that the U-band isidle, the BS may transmit the initial signal to the UE in the U-band.

The UE receives the initial signal from the BS in the U-band (S1920 andS2020).

The BS transmits a DL Tx burst related to the initial signal and a PDCCHto the UE in the U-band (S1930 and S2130). The PDCCH included in the DLTx burst may be transmitted to the UE at a predetermined periodicityduring the transmission of the DL Tx burst.

The UE performs second PDCCH monitoring at a second periodicity, whichis different from the first periodicity, in the U-band (S1940 andS2030). The UE performs the second PDCCH monitoring from a slot after Nslots with respect to a slot in which the initial signal is receivedduring the transmission of the DL Tx burst.

Although FIG. 19 illustrates the initial signal transmission and the DLTx burst and PDCCH transmission at the BS as different steps, theinitial signal transmission and the DL Tx burst and PDCCH transmissionmay be performed simultaneously or sequentially. In addition, the PDCCHmonitoring at the UE, which is performed at the second periodicity inthe U-band, and the DL Tx burst and PDCCH transmission at the BS in theU-band may be performed at the same time. Alternatively, the operationsmay be performed in the reverse order to that shown in FIG. 19 .

By operating as described above, the BS and UE may transmit and receivethe PDCCH at the second periodicity while the BS transmit the DL Txburst as shown in FIG. 18 , thereby reducing the complexity of the PDCCHmonitoring at the UE and the battery consumption thereof.

In the present disclosure, the second periodicity may correspond to oneslot duration.

For example, the second PDCCH monitoring based on the second periodicitymay include monitoring the PDCCH at the second periodicity at a slotboundary at which each slot starts.

The first periodicity may be set shorter than the second periodicity. Inthis case, the first periodicity may be indicated or configured byphysical layer signaling or higher layer signaling. Thus, afterreceiving the initial signal, the UE may perform the PDCCH monitoring ata periodicity longer than the previous one.

In the present disclosure, first PDCCH candidates for the first PDCCHmonitoring based on the first periodicity at the slot boundary at whicheach slot starts may have a relationship of inclusion with second PDCCHcandidates for the second PDCCH monitoring based on the secondperiodicity. For example, the first PDCCH candidates may include thesecond PDCCH candidates and vice versa.

In the present disclosure, the initial signal may be one of thefollowing:

-   -   an SS modified for extension in the frequency domain;    -   a DM-RS for a PBCH modified for the extension in the frequency        domain;    -   a DM-RS for the PDCCH;    -   a group common PDCCH;    -   a cell-specific CSI-RS; and    -   a CP for some symbols of the DL Tx burst or a part of the CP.

Here, the group common PDCCH may correspond to a PDCCH including slotformat indicator (SFI) information.

Thus, upon receiving the group common PDCCH as the initial signal, theUE may perform the following steps: detecting a DM-RS for the groupcommon PDCCH; decoding the group common PDCCH based on the DM-RS; andobtaining the presence of the DL Tx burst from the BS by checkingwhether the CRC result for the group common PDCCH is successful.

Since each of the examples of the proposed methods may be included asone method for implementing the present disclosure, it is apparent thateach example may be regarded as a proposed method. Although the proposedmethods may be implemented independently, some of the proposed methodsmay be combined (or merged) for implementation. In addition, it may beregulated that information on whether the proposed methods are applied(or information on rules related to the proposed methods) should betransmitted from a BS to a UE through a predefined signal (e.g., aphysical layer signal, a higher layer signal, etc.).

5. DEVICE CONFIGURATION

FIG. 22 is a block diagram illustrating the configurations of a UE and aBS for implementing the proposed embodiments. The UE and the BSillustrated in FIG. 22 operate to implement the embodiments of theafore-described method of transmitting and receiving a signal in aU-band.

A UE 1 may act as a transmission end on a UL and as a reception end on aDL. A BS (eNB or gNB) 100 may act as a reception end on a UL and as atransmission end on a DL.

That is, each of the UE and the BS may include a Transmitter (Tx) 10 or110 and a Receiver (Rx) 20 or 120, for controlling transmission andreception of information, data, and/or messages, and an antenna 30 or130 for transmitting and receiving information, data, and/or messages.

Further, each of the UE and the BS includes a processor 40 or 140 forimplementing the afore-described embodiments of the present disclosure.The processor 40 or 140 may be configured to perform the foregoingdescribed/proposed procedures and/or methods by controlling the memory50 or 150 and/or the Tx 10 or 110 and/or the Rx 20 or 120.

For example, the processor 40 or 140 includes a communication modemdesigned to implement wireless communication technologies (e.g., LTE andNR). The memory 50 or 150 is coupled to the processor 40 or 140, andstores various types of information related to operations of theprocessor 40 or 140. For example, the memory 50 or 150 may storesoftware code including instructions for performing all or part ofprocesses controlled by the processor 40 or 140 or theafore-described/proposed procedures and/or methods. The Tx 10 or 110and/or the Rx 20 or 120 is coupled to the processor 40 or 140 andtransmits and/or receives a wireless signal. The processor 40 or 140 andthe memory 50 or 150 may be part of a processing chip (e.g., system onchip (SoC)).

A processor of a communication device for transmitting or receiving a DLsignal according to the present disclosure may operate as follows bycontrolling a memory.

The processor of the communication device for receiving the DL signalfrom the BS in a U-band may be configured to: receive the DL signal byperforming first PDCCH monitoring at a first periodicity in the U-band;receive an initial signal indicating the presence of a DL Tx burst fromthe BS in the U-band; and receive the DL signal by performing secondPDCCH monitoring at a second periodicity, which is different from thefirst periodicity, in the U-band, wherein the second PDCCH monitoring isperformed from a slot after N slots with respect to a slot in which theinitial signal is received during transmission of the DL Tx burst.

The UE 1 including the communication device may be configured to controlthe processor 40 and the Rx 20 to receive the DL signal by performingthe first PDCCH monitoring at the first periodicity in the U-band;receive the initial signal indicating the presence of the DL Tx burstfrom the BS in the U-band; and receive the DL signal by performing thesecond PDCCH monitoring at the second periodicity, which is differentfrom the first periodicity, in the U-band, wherein the second PDCCHmonitoring is performed from the slot after the N slots with respect tothe slot in which the initial signal is received during the transmissionof the DL Tx burst.

The processor of the communication device for transmitting the DL signalto the UE in the U-band may be configured to: perform a CAP fortransmitting the DL signal in the U-band; and transmit the initialsignal and the DL Tx burst including a PDCCH in the U-band based on theCAP. The PDCCH included in the DL Tx burst may be transmitted to the UEat a predetermined periodicity during the transmission of the DL Txburst.

The BS 100 including the communication device may be configured tocontrol the processor 140, the Tx 110, and the Rx 120 to perform the CAPfor transmitting the DL signal in the U-band; and transmit the initialsignal and the DL Tx burst including the PDCCH in the U-band based onthe CAP. The PDCCH included in the DL Tx burst may be transmitted to theUE at the predetermined periodicity during the transmission of the DL Txburst.

The Tx and Rx of the UE and the BS may perform packetmodulation/demodulation for data transmission, high-speed packet channelcoding, OFDM packet scheduling, TDD packet scheduling, and/or channelmultiplexing. Each of the UE and the BS of FIG. 22 may further include alow-power radio frequency/intermediate frequency (RF/IF) module.

Meanwhile, the UE may be any of a Personal Digital Assistant (PDA), acellular phone, a Personal Communication Service (PCS) phone, a GlobalSystem for Mobile (GSM) phone, a Wideband Code Division Multiple Access(WCDMA) phone, a Mobile Broadband System (MBS) phone, a hand-held PC, alaptop PC, a smart phone, a Multi Mode-Multi Band (MM-MB) terminal, etc.

The smart phone is a terminal taking the advantages of both a mobilephone and a PDA. It incorporates the functions of a PDA, that is,scheduling and data communications such as fax transmission andreception and Internet connection into a mobile phone. The MB-MMterminal refers to a terminal which has a multi-modem chip built thereinand which can operate in any of a mobile Internet system and othermobile communication systems (e.g. CDMA 2000, WCDMA, etc.).

Embodiments of the present disclosure may be achieved by various means,for example, hardware, firmware, software, or a combination thereof.

In a hardware configuration, the methods according to exemplaryembodiments of the present disclosure may be achieved by one or moreApplication Specific Integrated Circuits (ASICs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, microcontrollers, microprocessors,etc.

In a firmware or software configuration, the methods according to theembodiments of the present disclosure may be implemented in the form ofa module, a procedure, a function, etc. performing the above-describedfunctions or operations. A software code may be stored in the memory 50or 150 and executed by the processor 40 or 140. The memory is located atthe interior or exterior of the processor and may transmit and receivedata to and from the processor via various known means.

Those skilled in the art will appreciate that the present disclosure maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent disclosure. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of thedisclosure should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein. It is obvious to those skilled in the art thatclaims that are not explicitly cited in each other in the appendedclaims may be presented in combination as an embodiment of the presentdisclosure or included as a new claim by a subsequent amendment afterthe application is filed.

The present disclosure is applicable to various wireless access systemsincluding a 3GPP system, and/or a 3GPP2 system. Besides these wirelessaccess systems, the embodiments of the present disclosure are applicableto all technical fields in which the wireless access systems find theirapplications. Moreover, the proposed method can also be applied tommWave communication using an ultra-high frequency band.

What is claimed is:
 1. A method for monitoring search space set by auser equipment (UE) in a wireless communication system, the methodcomprising: monitoring a first search space set; and monitoring a secondsearch space set from a second slot after at least one slot from a firstslot of the first search space set based on a Physical Downlink ControlChannel (PDCCH) being detected in the first slot, wherein the monitoringof the first search space set is stopped based on a Channel OccupancyTime (COT).
 2. The method of claim 1, wherein the PDCCH comprises a slotformat indicator (SFI) including information related to configuration ofOrthogonal Frequency Division Multiplexing (OFDM) symbols included inthe COT, wherein each of the OFDM symbols is configured as one ofdownlink, uplink and flexible.
 3. The method of claim 1, wherein themonitoring of the first search space set is stopped after at least oneslot from the COT.
 4. The method of claim 1, wherein the first searchspace set is different from the second search space set.
 5. The methodof claim 1, wherein the COT is informed by the PDCCH.
 6. The method ofclaim 1, wherein the monitoring of the second search space set isperformed within the COT.
 7. A user equipment (UE) for monitoring searchspace set in a wireless communication system, the UE comprising: atleast one transceiver; at least one processor; and at least one computermemory operably connectable to the at least one processor and storinginstructions that, when executed, cause the at least one processor toperform operations comprising: monitoring a first search space set; andmonitoring a second search space set from a second slot after at leastone slot from a first slot of the first search space set based on aPhysical Downlink Control Channel (PDCCH) being detected, through the atleast one transceiver, in the first slot, wherein the monitoring of thefirst search space set is stopped based on a Channel Occupancy Time(COT).
 8. The UE of claim 7, wherein the PDCCH comprises a slot formatindicator (SFI) including information related to configuration ofOrthogonal Frequency Division Multiplexing (OFDM) symbols included inthe COT, wherein each of the OFDM symbols is configured as one ofdownlink, uplink and flexible.
 9. The UE of claim 7, wherein themonitoring of the first search space set is stopped after at least oneslot from the COT.
 10. The UE of claim 7, wherein the first search spaceset is different from the second search space set.
 11. The UE of claim7, wherein the COT is informed by the PDCCH.
 12. The UE of claim 7,wherein the monitoring of the second search space set is performedwithin the COT.
 13. A non-transitory computer readable storage mediumstoring at least one computer program comprising instructions that, whenexecuted by at least one processor, cause the at least one processor toperform operations, the operations comprising: monitoring a first searchspace set; and monitoring a second search space set from a second slotafter at least one slot from a first slot of the first search space setbased on a Physical Downlink Control Channel (PDCCH) being detected inthe first slot, wherein the monitoring of the first search space set isstopped based on a Channel Occupancy Time (COT).
 14. An apparatus formonitoring search space set in a wireless communication system, theapparatus comprising: at least one processor; and at least one computermemory operably connectable to the at least one processor and storinginstructions that, when executed, cause the at least one processor toperform operations comprising: monitoring a first search space set; andmonitoring a second search space set from a second slot after at leastone slot from a first slot of the first search space set based on aPhysical Downlink Control Channel (PDCCH) being detected in the firstslot, wherein the monitoring of the first search space set is stoppedbased on a Channel Occupancy Time (COT).